Fine zinc oxide particles, process for producing the same, and use thereof

ABSTRACT

A process for producing zinc oxide fine particles comprising heating a mixture comprising a zinc source, a carboxyl-containing compound, and an alcohol; a process for producing zinc oxide-polymer composite particles, which comprises heating a mixture comprising a zinc source, a carboxyl-containing compound, a polymer, and an alcohol at a temperature of 100° C. or higher; a process for producing inorganic compound particles having on their surface a cluster of thin plate like zinc oxide crystals with their tip projecting outward, which comprises heating a mixture comprising a zinc source, a carboxyl-containing compound, lactic acid or a compound thereof, and an alcohol at a temperature of 100° C. or higher; a process for producing zinc oxide-based particles comprising heating a mixture comprising a zinc source, a carboxyl-containing compound, at least one element additive selected from the group consisting of the group IIIB metal elements and the group IVB metal elements, and an alcohol at a temperature of 100° C. or higher; zinc oxide-based fine particles obtained by these processes; and uses of the zinc oxide-based fine particles.

TECHNICAL FIELD

This invention relates to a process for producing zinc oxide-based fineparticles which are useful as a raw material or an additive for rubbervulcanization accelerators, various coatings, printing inks, colors,glass, catalysts, medicines, pigments, ferrite, etc. and can also bemade use of in electrophotographic photoreceptors, printing materials,platemaking materials, UV screens, UV absorbing materials, gas sensors,etc. It also relates to a process for producing zinc oxide-based fineparticles which are useful as such an additive that has highlight-transmitting properties in the visible region and high UVabsorbing properties, i.e., a so-called transparent UV absorber incoating materials, varnishes, resins, paper, cosmetics, and the like.

The present invention relates to zinc oxide-based fine particles havinghigh transparency in the visible region, excellent UV absorbingproperties, and heat ray screening properties as well as theabove-mentioned functions and uses, which are useful as a so-calledtransparent UV and heat ray screening agent, an electrically conductingagent or an antistatic agent that in coatings (e.g., coating agent, ink,etc.), resins, paper, cosmetics, etc.; a process for producing the same;and products containing the same, i.e., coatings, coated articles, resincompositions, resin molded articles, cosmetics, and paper.

The present invention relates to zinc oxide-based fine particles whichhave a unique higher-order structure in which the constituent primaryparticles (zinc oxide crystals) have a controlled size and thereforeexhibit high light transmitting properties combined with excellentscattering properties in the visible region, that is, excellent diffusetransmission properties in addition to the above-described functions anduses. The fine particles are therefore useful as a light diffusingagent. The invention also relates to a process for producing such zincoxide-based particles and products containing the same, such as coatings(e.g., coating agent, ink, etc.), coated articles, resin compositions,resin molded articles, cosmetics, and paper, typified by a medium fordiffuse transmission, such as a diffuser film for back-lighting liquidcrystal displays.

The present invention relates to zinc oxide-based fine particles whichnot only have the above-described functions and uses but have controlledcrystal morphology and a unique agglomerated state (higher-orderstructure) and are therefore also excellent in antimicrobial propertiesand deodorizing properties; a process for producing the same; andproducts containing the same, such as coatings (e.g., coating agent,ink, etc.), coated articles, resin compositions, resin molded articles,cosmetics, and paper.

BACKGROUND ART

Zinc oxide fine particles, what we call zinc white, have beenconventionally produced by (1) a method consisting of gas phaseoxidation of zinc vapor (called a France process or a American process)or (2) a method comprising reacting a zinc salt and an alkali metalcarbonate in an aqueous solution to obtain zinc carbonate powder and,after washing with water and drying, pyrolyzing the powder in air. Zincoxide obtained by the method (1) appears to have a particle size ofsubmicron order but undergoes strong secondary agglomeration during theproduction process. Dispersing the particles in coating compositions orresin compositions requires much mechanical labor and yet results in afailure of obtaining a homogeneous dispersion. Compared with the method(1), the method (2) provides such finer particles as have a primaryparticle size of 0.1 μm or smaller, but the effects expected from thefineness are not manifested sufficiently on account of the strongagglomerating force among primary particles. Under the presentsituation, it is still less achievable with these methods to obtain zincoxide fine particles with strictly controlled morphology, such asparticle size, shape and surface condition of the primary particles, andthe state of dispersion or agglomeration, in agreement with the end use.

In recent years, development of zinc oxide-based fine particlespractically having a particle size of not greater than 0.1 μm has beendemanded for use as a weatherable and heat-resistant material which ishighly transparent in the visible region and also capable of absorbingultraviolet light, i.e., a so-called transparent UV absorber. Processeshitherto proposed for producing such fine particles include (3) a methodcomprising gas phase oxidation of zinc vapor and (4) a wet process, suchas a process comprising hydrolysis of a zinc salt in an alkali aqueoussolution (see JP-A-4-164813 and JP-A-4-357114, the term “JP-A” as usedherein means an “unexamined published Japanese patent application”) anda process in which a mixed solution of an acidic salt of zinc andammonium acetate and hydrogen sulfide are subjected to autoclaving toform zinc sulfide, which is then subjected to oxidation (seeJP-A-2-311314). The fine particles as obtained by the method (3) arepowder having undergone firm secondary agglomeration as stated aboveand, when added to plastic moldings, such as fiber, a plate or a film,or coatings for the purpose of imparting UV absorptivity or improvingweatherability, fail to provide products having satisfactorytransparency. Further, when the fine particles are dispersed in anappropriate solvent and, if necessary, mixed with a binder resin toprepare a coating agent, and the coating agent is applied to atransparent substrate, such as glass or a plastic film, for the purposeof imparting UV absorptivity, the resulting coating film has poortransparency and homogeneity. On the other hand, the wet processes (4)involve complicated steps and unavoidably incur high cost. Thus, aprocess for producing zinc oxide-based fine particles which manifest thefunctions and characteristics of fine particles to the full extent andstill have general-purpose properties is unknown.

Since zinc oxide fine particles have excellent UV screening power (inabsorbing or scattering), they are used in coating films or resin moldedarticles endowed with UV screening power. However, zinc oxide fineparticles have low dispersibility due to their liability toagglomeration.

Light-diffusing compositions comprising transparent inorganic fineparticles, e.g., calcium carbonate, silica or barium sulfate, asdispersed in a binder component capable of dispersing such fineparticles (e.g., methacrylic resins) are known. The light-diffusingcompositions are used as a coating composition to be applied to atransparent substrate to form a light-diffusing layer or as a moldingmaterial to be molded into a molded article having light-diffusingproperties, to provide a diffuser. The diffusing properties of thesediffusers are based on light scattering at the interface between theinorganic transparent fine particles and the binder component due to thedifference in refractive index therebetween.

However, the inorganic transparent particles of calcium carbonate,silica, barium sulfate, and the like do not have a UV screeningfunction. Further, these diffusers essentially have poor mechanicalcharacteristics on account of low affinity between the inorganictransparent particles and the binder component. Furthermore, since thediffusers should contain a large quantity of the inorganic transparentparticles for achieving high diffusing properties, they have a reducedpercent transmission and further reduced mechanical characteristics.

There has recently been an increasing demand for antistatic treatment onglass products or plastic products (films and fibers) for use as windowpanes of a clean room, CRT screens, flooring, wall covering, clothing,and the like for the purpose of preventing adhesion of dust.

An insulator, such as resin, can be made electrically conductive by, forexample, dispersing a conducting agent in resin or applying a coatingcomposition having dispersed therein a conducting agent on a substrateto form an electrically conductive layer. Known conducting agentsinclude fine particles of metals, e.g., nickel (Ni), copper (Cu) oraluminum (Al); fine particles of metal oxides, such as those obtained byreducing metal oxides represented by titanium black, and electricallyconducting white metal oxides activated with different elements (e.g.,tin oxide-based particles, indium oxide-based particles, and zincoxide-based particles); carbonaceous fine particles of carbon black,graphite, etc.; and organic conducting agents represented by nonionic,anionic, cationic or amphoteric surface active agents.

Of these conducting agents, organic ones, whose conductivity-impartingaction is based on ionic conduction and therefore dependent on humidity,unsuccessfully work at a low humidity. Besides, those having a lowmolecular weight bleed out with time and undergo deterioration inperformance.

To the contrary, metallic, metal oxide type, or carbonaceous conductingagents, whose action is based on electron conduction, are substantiallyindependent on humidity. Although superior to organic ones in thispoint, the metal oxide conducting agents obtained by reduction oftitanium black, etc. and the carbonaceous conducting agents assume ablack or nearly black color, and the metallic conducting agents reflectvisible light strongly. Therefore, it is extremely difficult to retainthe transparency of the substrate or matrix, and the application ofthese conducting agents is so limited.

On the other hand, it is known that a coating film formed of ink or acoating composition having dispersed therein such white conductingparticles as antimony-doped tin oxide and tin-doped indium oxide or afilm formed of a resin composition having dispersed therein theseparticles successfully impart conductivity for producing antistaticeffect without impairing the hue of the substrate or the matrix. A filmformed of these oxides by gas phase film formation, such as sputtering,has high electrical conductivity and has been used as a transparentelectrode of flat displays, such as liquid crystal displays andelectroluminescence displays, an electrode for touch panels of wordprocessors, electronic game equipment, etc., and an antistatic film.However, because the raw materials of tin oxide- or indium oxide-basedparticles are very expensive, and gas phase film formation requiresexpensive equipment, this technique does not seem applicable generally.

In recent times, a material has been demanded, which can be applied toor incorporated into glass products, such as window panes, or resinproducts, such as polyester or (meth)acrylic films or sheets, withoutimpairing the transparency or hue of the substrate or matrix andeffectively shield these products from ultraviolet rays, inclusive ofUV-B (280 to 320 nm) and UV-A (320 to 400 nm), and heat rays.

Conventional materials known for their UV screening effect includeorganic UV absorbers, such as benzotriazole compounds and benzophenonecompounds, and inorganic UV absorbers, such as titanium oxide, zincoxide, and cerium oxide. However, none of them has a heat ray screeningeffect.

Known heat ray screens include organic dyes having absorptivity in theinfrared region, such as anthraquinone type, polymethine type, cyaninetype, aluminum type or diimonium type dyes, and the aforementioned tinoxide- or indium oxide-based conducting particles, but none of themscreens out ultraviolet rays effectively.

It is known that fine particles of mica coated with a titanium oxidethin film absorb ultraviolet light owing to the titanium oxide coat and,having a multi-layer structure, scatter electromagnetic waves in theheat ray region to some extent. However, the particles have insufficientvisible light transmitting properties and are not deemed to fit theabove-described needs.

Considering a combined use of a UV screen and a heat ray screen, thereare disadvantages such that the organic dye (heat ray screen) showsabsorptions in the visible light and unavoidably causes coloring; theheat ray absorption range of the organic dye is narrow; and the tinoxide- or indium oxide-based particles are expensive and economicallydisadvantageous as stated above.

Zinc oxide effectively absorbs both A and B waves of ultraviolet lightand shows no selective absorption in the visible region. Therefore, athin film having highly dispersed therein ultrafine particles of zincoxide or a homogeneous zinc oxide thin film obtained by gas phase filmformation serves as a transparent UV absorbing film. Doping of zincoxide with a trivalent or tetravalent metal element gives zinc oxideelectrical conductivity and, in some cases, heat ray screeningproperties.

However, as stated above, a process for producing zinc oxide fineparticles which can manifest the functions and characteristics of fineparticles to the full extent and still have general-purpose propertiesis unknown. Besides, all the zinc oxide fine particles so far obtainedby conventional processes have UV absorbing properties but cannot screenout (near) infrared rays.

On the other hand, it is known that a zinc oxide film comprising zincoxide doped with aluminum (Al) which is obtained by gas phase filmformation exhibits high electrical conductivity and heat ray screeningpower (see Minami Uchitsugu, Ohyo Butsuri (Applied Physics), Vol. 61,No. 12 (1992)). It has been suggested that a solid solution of silicon(Si), germanium (Ge), zirconium (Zr), etc. in zinc oxide (JP-B-5-6766,the term “JP-B” as used herein means an “examined published Japanesepatent application”), a solid solution of the group IIIB element, e.g.,boron (B), scandium (Sc), yttrium (Y), indium (In), thallium (Tl), etc.,in zinc oxide (JP-B-3-72011) or a solid solution of aluminum (Al) inzinc oxide (JP-B-4-929) can provide a transparent zinc oxide filmexcellent in conductivity and infrared reflecting properties. However,any of the techniques disclosed consists of gas phase film formation andcannot be a general-purpose process.

It is also known that an electrically conductive zinc oxide film can beobtained by a method for forming a zinc oxide thin film making use ofpyrolysis of a zinc salt, in which the film is finally subjected to hightemperature in a reducing atmosphere, or a dopant is previously added toa zinc salt solution and a resulting film is finally subjected to hightemperature, as disclosed in JP-A-1-301515. This method still fails toprovide heat ray screening properties.

Additional methods which are generally known for making zinc oxidepowder electrically conductive include a method comprising calciningzinc oxide powder at a high temperature in a reducing atmosphere and amethod comprising calcining zinc oxide powder mixed with a dopant, e.g.,aluminum oxide, at a high temperature in a reducing atmosphere. Thedegree of conductivity attained by the former method is limited. Ineither method, because the particles are exposed to high temperature,fine particles, especially ultrafine particles of 0.1 μm or smallercannot be obtained.

A transparent conducting film-forming composition containing conductivezinc oxide fine powder prepared by a specific process is known(JP-A-1-153769), in which the conductive zinc oxide fine powder isaluminum-activated powder having a specific surface area diameter of notgreater than 0.1 μm and a volume resistivity of not higher than 10⁴ Ωcmunder a specific pressure condition. However, since the preparation ofthe zinc oxide powder involves calcination at a high temperature, thepowder, even having a specific surface area diameter of not greater than0.1 μm, becomes larger as dispersed in the composition. It is assumedthat the film obtained by application of the coating composition wouldhave limited transparency. Heat ray screening properties of the filmaccording to this technique are unknown.

Fine and thin particles of inorganic compounds having a tabular form, aflaky form and the like include titanium oxide fine particles(JP-A-58-88121), titanium oxide-coated mica (JP-B-31-9355, JP-B-33-294,and JP-A-2-173060), and zinc oxide fine flakes (JP-B-55-25133 andJP-A-6-80421).

These inorganic compound fine particles are added to resin compositionsforming film, fiber or plates; coating compositions to be applied tofilm, fiber, resin plates, glass, paper, etc.; paper; cosmetics; and thelike for the purpose of adding value to these products.

Inorganic compound fine particles which are added to resin compositionsforming film, fiber or plates; coating compositions to be applied tofilm, fiber, resin plates, glass, paper, etc.; paper; cosmetics; and thelike for the purpose of improving appearance, energy saving, andimproving comfort of household goods in conformity with an advancedstyle of life are required to have:

(1) an attractive appearance brought about by designing to the effectthat a tone changes with a change in viewing angle or angle of lightincidence and also by transparency; and

(2) a function of efficiently cutting heat rays, particularly nearinfrared rays, in seeking energy saving and comfort.

For protection of the body, particularly hair, eyes and the skin and forprevention of deterioration of resin products, the inorganic compoundfine particles possessing the above characteristics (1) and (2) areadditionally required to have (3) a function of efficiently cuttingultraviolet rays which are contained in sunlight or electromagneticwaves emitted from fluorescent tubes and cause harm to the body anddeterioration in resin products. UV screens comprising inorganiccompound fine particles are superior to organic UV absorbers in terms oftoxicity, heat resistance, and stability with time. From this viewpoint,TiO₂ or ZnO has been made into ultrafine particles or thin particles foruse for transparency improvement.

Ultrafine or thin titanium oxide particles do not possess theabove-described effects of design, though having a UV cutting effect andhigher visible light transmitting properties than titanium white that isa white pigment.

Although titanium oxide-coated mica is capable of preventingtransmission of heat rays and ultraviolet rays, they have a pearlyluster, lacking transparency, and is therefore inferior in terms of theabove-mentioned attractiveness of appearance.

Ultrafine or thin plate like zinc oxide particles have transparency tovisible light and, as compared with titanium oxide fine particles, cutultraviolet rays over a longer wavelength side, and retain the UVcutting effect over an extended time period. However, zinc oxide fineparticles do not possess the above-described effect of design andtransmit heat rays.

An object of the present invention is to provide a highly productiveprocess for producing zinc oxide fine particles with their size, shapeand surface conditions controlled and also with the degree of dispersionand agglomeration controlled, which comprises heating a mixture of zincor a compound thereof, a carboxyl-containing compound, and an alcohol.

Another object of the invention is to provide an industrial process forproducing zinc oxide fine particles which can manifest the functions andcharacteristics of fine particles having excellent transparency to thefull extent in practical use.

Still another object of the invention is to provide zinc oxide-polymercomposite particles which exhibit UV screening power, controlled visiblelight transmitting properties combined with controlled light diffusingproperties, and excellent dispersibility.

Yet another object of the invention is to provide a process forproducing such zinc oxide-polymer composite particles with satisfactoryproductivity.

A further object of the invention is to provide inorganic compoundparticles which show abnormal light transmitting properties ascribed totheir unique geometrical characteristics not heretofore attained.

A still further object of the invention is to provide a process forproducing such inorganic compound particles with satisfactoryproductivity.

A yet further object of the invention is to provide zinc oxide-basedparticles which comprise zinc oxide having excellent UV screeningproperties as a base to which heat ray screening properties andelectrical conductivity are imparted, and which are easily madetransparent.

A yet another object of the invention is to provide a process forproducing such zinc oxide-based particles with high productivity.

A yet another object of the invention is to provide coatingcompositions, coated articles, resin compositions, resin moldedarticles, paper, and cosmetics which contain the above-described zincoxide fine particles, zinc oxide-polymer composite particles, inorganiccompound particles or zinc oxide-based particles so that thecharacteristics possesses by these particles may be taken advantage of.

DISCLOSURE OF THE INVENTION

The inventors of the present invention have conducted extensiveinvestigations in order to accomplish the above objects and, as aresult, reached the invention.

The invention embraces the following embodiments.

(1) A process for producing zinc oxide fine particles comprising heatinga mixture comprising a zinc source, a carboxyl-containing compound, andan alcohol.

(2) A process for producing zinc oxide fine particles as described in(1), which comprises a first mixing step of preparing a first mixturecomprising a zinc source and a carboxyl-containing compound and a secondmixing step of mixing the first mixture with a heated alcohol-containingsolution.

(3) A process for producing zinc oxide fine particles as described in(2), wherein the second mixing step is a step of adding the firstmixture to an alcohol-containing solution maintained at 100° C. or aboveand mixing them.

(4) A process for producing zinc oxide fine particles as described inany of (1) to (3), wherein the process comprises a first mixing step ofpreparing a first mixture comprising a zinc source and acarboxyl-containing compound, a second mixing step of mixing the firstmixture maintained at 60° C. or above with an alcohol-containingsolution maintained at 100° C. or above to obtain a second mixture, anda step of heating the second mixture.

(5) A process for producing zinc oxide fine particles as described inany of (1) to (4), wherein the resulting zinc oxide fine particles havean average primary particle size ranging from 0.005 to 10 μm.

(6) A process for producing zinc oxide fine particles as described inany of (1) to (5), wherein the zinc source is selected from the groupconsisting of zinc oxide, zinc hydroxide, and zinc acetate.

(7) A process for producing zinc oxide fine particles as described inany of (1) to (6), wherein the carboxyl-containing compound comprises asaturated fatty acid having a boiling point of 200° C. or lower atatmospheric pressure.

(8) A process for producing zinc oxide fine particles as described inany of (4) to (7), wherein the second mixing step and/or the heatingstep is/are carried out in the presence of a compound additivecontaining one or more than one atomic group of at least one kindselected from the group consisting of a carboxyl group, an amino group,a quaternary ammonio group, an amido group, an imido bond, a hydroxylgroup, a carboxylic acid ester bond, a urethane group, a urethane bond,a ureido group, a ureylene bond, an isocyanate group, an epoxy group, aphosphoric acid group, a metallic hydroxyl group, a metallic alkoxygroup, and a sulfonic acid group in the molecule thereof and having amolecular weight of less than 1,000.

(9) A process for producing zinc oxide fine particles as described inany of (4) to (8), wherein the second mixing step or the heating step iscarried out in the presence of carbon dioxide and/or a carbonic acidsource.

(10) A process for producing zinc oxide-polymer composite particles,which comprises heating a mixture comprising a zinc source, acarboxyl-containing compound, a polymer, and an alcohol at a temperatureof 100° C. or higher.

(11) A process for producing zinc oxide-polymer composite particles asdescribed in (10), wherein the process comprises a first mixing step ofpreparing a first mixture comprising a zinc source and acarboxyl-containing compound and a second mixing step of mixing thefirst mixture with a heated alcohol-containing solution, and the polymeris added in at least one step selected from the first mixing step andthe second mixing step.

(12) A process for producing zinc oxide-polymer composite particles asdescribed in (10) or (11), wherein the process comprises a first mixingstep of preparing a first mixture comprising a zinc source and acarboxyl-containing compound, a second mixing step of mixing the firstmixture maintained at 60° C. or above with an alcohol-containingsolution maintained at 100° C. or above to obtain a second mixture, anda step of heating the second mixture, and the polymer is added in atleast one step selected from the first mixing step, the second mixingstep, and the heating step.

(13) A process for producing zinc oxide-polymer composite particles asdescribed in (11), wherein the first mixing step is a step of dissolvingthe zinc source in a mixed solvent of the carboxyl-containing compoundand water.

(14) A process for producing zinc oxide-polymer composite particles asdescribed in any of (10) to (13), wherein the polymer contains at leastone polar atomic group.

(15) A process for producing zinc oxide-polymer composite particles asdescribed in (14), wherein the atomic group is at least one memberselected from the group consisting of a carboxyl group, an amino group,a quaternary ammonio group, an amido group, an imido bond, a hydroxylgroup, a carboxylic acid ester bond, a urethane group, a urethane bond,a ureido group, a ureylene bond, an isocyanate group, an epoxy group, aphosphoric acid group, a metallic hydroxyl group, a metallic alkoxygroup, and a sulfonic acid group.

(16) A process for producing zinc oxide-polymer composite particles asdescribed in any of (10) to (15), wherein the zinc source is selectedfrom the group consisting of zinc oxide, zinc hydroxide, and zincacetate.

(17) A process for producing zinc oxide-polymer composite particles asdescribed in any of (10) to (16), wherein the carboxyl-containingcompound comprises a saturated fatty acid having a boiling point of 200°C. or lower at atmospheric pressure.

(18) A process for producing zinc oxide-polymer composite particles asdescribed in any of (10) to (17), wherein the polymer is used at aweight ratio of 0.01 to 1.0 to the zinc atoms, in terms of zinc oxide,present in the zinc source.

(19) A process for producing inorganic compound particles having ontheir surface a cluster of thin plate like zinc oxide crystals withtheir tip projecting outward, which comprises heating a mixturecomprising a zinc source, a carboxyl-containing compound, lactic acid ora compound thereof, and an alcohol at a temperature of 100° C. orhigher.

(20) A process for producing inorganic compound particles as describedin (19), wherein the process comprises a first mixing step of preparinga first mixture comprising a zinc source and a carboxyl-containingcompound and a second mixing step of mixing the first mixture with aheated alcohol-containing solution, and the lactic acid or a compoundthereof is added in at least one step selected from the first mixingstep and the second mixing step.

(21) A process for producing inorganic compound particles described in(19), wherein the process comprises a first mixing step of preparing afirst mixture comprising a zinc source and a carboxyl-containingcompound, a second mixing step of mixing the first mixture maintained at60° C. or above with an alcohol-containing solution maintained at 100°C. or above to obtain a second mixture, and a heating step of heatingthe second mixture, and the lactic acid or a compound thereof is addedin at least one step selected from the first mixing step, the secondmixing step, and the heating step.

(22) A process for producing inorganic compound particles as describedin (21), wherein the first mixing step is a step of dissolving the zincsource in a mixed solvent of the carboxyl-containing compound and water.

(23) A process for producing inorganic compound particles as describedin any of (19) to (22), wherein the lactic acid or a compound thereof isat least one compound selected from the group consisting of lactic acid,a lactic acid metal salt, and a lactic ester.

(24) A process for producing inorganic compound particles as describedin any of (19) to (23), wherein the zinc source is selected from thegroup consisting of zinc oxide, zinc hydroxide, and zinc acetate.

(25) A process for producing inorganic compound particles as describedin any of (19) to (24), wherein the carboxyl-containing compoundcomprises a saturated fatty acid having a boiling point of 200° C. orlower at atmospheric pressure.

(26) A process for producing inorganic compound particles as describedin any of (20) to (25), wherein the lactic acid or a compound thereof isused at a lactic acid to zinc molar ratio of 0.001 to 0.4.

(27) A process for producing zinc oxide-based particles comprisingheating a mixture comprising a zinc source, a carboxyl-containingcompound, at least one element additive selected from the groupconsisting of the group IIIB metal elements and the group IVB metalelements, and an alcohol at a temperature of 100° C. or higher.

(28) A process for producing zinc oxide-based particles as described in(27), wherein the process comprises a first mixing step of preparing afirst mixture comprising a zinc source and a carboxyl-containingcompound and a second mixing step of mixing the first mixture with aheated alcohol-containing solution, and the element additive is added inat least one step selected from the first mixing step and the secondmixing step.

(29) A process for producing zinc oxide-based particles as described in(27) or (28), wherein the process comprises a first mixing step ofpreparing a first mixture comprising a zinc source and acarboxyl-containing compound, a second mixing step of mixing the firstmixture maintained at 60° C. or above with an alcohol-containingsolution maintained at 100° C. or above to obtain a second mixture, anda heating step of heating the second mixture, and the element additiveis added in at least one step selected from the first mixing step, thesecond mixing step, and the heating step.

(30) A process for producing zinc oxide-based particles as described inany of (27) to (29), wherein the group IIIB metal element is indiumand/or aluminum.

(31) A process for producing zinc oxide-based particles as described inany of (27) to (30), wherein the zinc source is selected from the groupconsisting of zinc oxide, zinc hydroxide, and zinc acetate.

(32) A process for producing zinc oxide-based particles as described inany of (27) to (31), wherein the carboxyl-containing compound comprisesa saturated fatty acid having a boiling point of 200° C. or lower atatmospheric pressure.

(33) A process for producing zinc oxide-based particles as described inany of (28) to (32), wherein any of the steps is conducted in thepresence of lactic acid or a compound thereof.

(34) A process for producing zinc oxide-based particles as described inany of (28) to (32), wherein any of the steps is conducted in thepresence of a polymer.

(35) A process for producing zinc oxide-based particles as described inany of (29) to (32), wherein the second mixing step and/or the heatingstep is/are carried out in the presence of a compound additivecontaining one or more than one atomic group of at least one kindselected from the group consisting of a carboxyl group, an amino group,a quaternary ammonio group, an amido group, an imido bond, a hydroxylgroup, a carboxylic acid ester bond, a urethane group, a urethane bond,a ureido group, a ureylene bond, an isocyanate group, an epoxy group, aphosphoric acid group, a metallic hydroxyl group, a metallic alkoxygroup, and a sulfonic acid group in the molecule thereof and having amolecular weight of less than 1,000.

(36) A process for producing zinc oxide-based particles as described inany of (29) to (32), wherein the second mixing step or the heating stepis carried out in the presence of carbon dioxide and/or a carbonic acidsource.

(37) Zinc oxide-polymer composite particles which comprise zinc oxidefine particles and a polymer, the proportion of the zinc oxide fineparticles being 50 to 99% by weight based on the total weight of thezinc oxide fine particles and the polymer, and the composite particleshaving an outer shell composed of a mixture and/or a composite of thezinc oxide fine particles and the polymer with the inside of the outershell being hollow.

(38) Zinc oxide-polymer composite particles as described in (37),wherein the composite particles have a number average particle size of0.1 to 10 μm with a coefficient of particle size variation being notmore than 30%.

(39) Zinc oxide-polymer composite particles as described in (38),wherein the zinc oxide fine particles have a number average particlesize of 0.005 to 0.1 μm, the ratio of the number average particle sizeof the zinc oxide fine particles to the number average particle size ofthe zinc oxide-polymer composite particles being {fraction (1/10)} to{fraction (1/1,000)}.

(40) Zinc oxide-polymer composite particles as described in any of (37)to (39), wherein the composite particles have a spherical shape and/oran ellipsoidal shape.

(41) Zinc oxide-polymer composite particles as described in any of (37)to (40), wherein the polymer contains at least one polar atomic group.

(42) Zinc oxide-polymer composite particles as described in (41),wherein the atomic group is at least one member selected from the groupconsisting of a carboxyl group, an amino group, a quaternary ammoniogroup, an amido group, an imido bond, a hydroxyl group, a carboxylicacid ester bond, a urethane group, a urethane bond, a ureido group, aureylene bond, an isocyanate group, an epoxy group, a phosphoric acidgroup, a metallic hydroxyl group, a metallic alkoxy group, and asulfonic acid group.

(43) Inorganic compound particles containing 60 to 100% by weight ofzinc oxide and having on their surface a cluster of thin plate like zincoxide crystals with their tip projecting outward.

(44) Inorganic compound particles as described in (43), wherein theparticles have a major axis/minor axis ratio of 1.0 to 5.0.

(45) Inorganic compound particles as described in (43) or (44), whereinthe particles have a number average particle size of 0.1 to 10 μm with acoefficient of particle size variation being not more than 30%.

(46) Inorganic compound particles as described in (43) to (45), whereinthe particles are hollow.

(47) Inorganic compound particles as described in (43) to (45), whereinthe particles are porous.

(48) Inorganic compound particles as described in any of (43) to (46),wherein the thin plate like zinc oxide crystals are thin plates having aflatness of 2 to 200.

(49) Inorganic compound particles as described in (48), wherein the thinplates have a major axis of 5 to 1,000 nm.

(50) Zinc oxide-based particles comprising a metal oxide co-precipitatecontaining, as a metallic component, at least one element additiveselected from the group consisting of the group IIIB metal elements andthe group IVB metal elements and zinc, having a zinc content of 80 to99.9% in terms of the ratio of the number of zinc atoms to the totalnumber of the atoms of the metallic components, and having X-raycrystallographically exhibiting zinc oxide crystalline properties.

(51) Zinc oxide-based particles as described in (50), wherein theelement additive is indium and/or aluminum.

(52) Zinc oxide-based particles as described in (50) or (51), whereinthe particles consist of single particles of the metal oxideco-precipitate.

(53) Zinc oxide-based particles in which the single particles describedin (52) form composite particles with a polymer.

(54) Zinc oxide-based particles as described in (52) or (53), whereinthe particles have an average shortest diameter of 0.001 to 0.1 μm.

(55) Zinc oxide-based particles which are secondary particles formed byagglomeration of primary particles, the primary particles being thesingle particles described in any of (52) to (54) which constitute thezinc oxide-based particles.

(56) Zinc oxide-based particles as described in (55), wherein thesecondary particles are hollow particles made up solely of an outershell.

(57) Zinc oxide-based particles as described in (55) or (56), whereinthe particles are hollow particles made up solely of an outer shellcomposed of the single particles and the polymer.

(58) Zinc oxide-based particles as described in any of (55) to (57),wherein the particles have an average particle size ranging from 0.001to 10 μm.

(59) A coating composition comprising zinc oxide fine particles producedby the process described in any of (1) to (9) and a binder componentcapable of forming a coating film binding the zinc oxide fine particles,the proportion of the zinc oxide fine particles being 0.1 to 99% byweight and the proportion of the binder component being 1 to 99.9% byweight each based on the total solids content of the zinc oxide fineparticles and the binder component.

(60) A coated article comprising at least one substrate selected fromthe group consisting of a resin molded article, glass and paper and acoating film provided on the substrate which is formed of the coatingcomposition described in (59).

(61) A resin composition comprising the zinc oxide fine particlesproduced by the process described in any of (1) to (9) and a resincapable of forming a continuous phase having dispersed therein the zincoxide fine particles, the proportion of the zinc oxide fine particlesbeing 0.1 to 99% by weight and the proportion of the resin being 1 to99.9% by weight each based on the total solids content of the zinc oxidefine particles and the resin.

(62) A resin molded article obtained by molding the resin compositiondescribed in (61) into at least one shape selected from the groupconsisting of a plate, a sheet, a film, and fiber.

(63) Paper comprising pulp made into paper and having dispersed thereinthe zinc oxide fine particles produced by the process described in anyof (1) to (9), the proportion of the zinc oxide fine particles being0.01 to 50% by weight based on the pulp.

(64) A cosmetic containing 0.1% by weight or more of the zinc oxide fineparticles produced by the process described in any of (1) to (9).

(65) A coating composition comprising the zinc oxide-polymer compositeparticles described in any of (37) to (42), a binder component capableof forming a transparent or semitransparent continuous phase, and asolvent capable of dispersing the composite particles and capable ofdispersing and/or dissolving the binder component.

(66) A coating composition comprising zinc oxide-polymer compositeparticles produced by the process described in any of (10) to (18), abinder component capable of forming a transparent or semitransparentcontinuous phase, and a solvent capable of dispersing the compositeparticles and capable of dispersing and/or dissolving the bindercomponent.

(67) A coated article comprising a transparent or semitransparentsubstrate and a coating film provided on the surface of the substratewhich is formed of the coating composition described in (65) or (66).

(68) A resin composition comprising the zinc oxide-polymer compositeparticles described in any of (37) to (42) and a resin capable offorming a transparent or semitransparent continuous phase.

(69) A resin composition comprising the zinc oxide-polymer compositeparticles produced by the process described in any of (10) to (18) and aresin capable of forming a transparent or semitransparent continuousphase.

(70) A resin molded article obtained by molding the resin compositiondescribed in (68) or (69) into at least one shape selected from thegroup consisting of a plate, a sheet, a film, and fiber.

(71) Paper comprising pulp made into paper and having dispersed thereinzinc oxide-polymer composite particles described in any of (37) to (42),the proportion of the composite particles being 0.01 to 50% by weightbased on the pulp.

(72) Paper comprising pulp made into paper and having dispersed thereinthe zinc oxide-polymer composite particles produced by the processdescribed in any of (10) to (18), the proportion of the compositeparticles being 0.01 to 50% by weight based on the pulp.

(73) A cosmetic containing 0.1% by weight or more of the zincoxide-polymer composite particles described in any of (37) to (42).

(74) A cosmetic containing 0.1% by weight or more of the zincoxide-polymer composite particles produced by the process described inany of (10) to (18).

(75) A diffuser for back-lighting a liquid crystal display, which has aresin layer containing the zinc oxide-polymer composite particlesdescribed in any of (37) to (42).

(76) A diffuser for back-lighting a liquid crystal display, which has aresin layer containing the zinc oxide-polymer composite particlesproduced by the process described in any of (10) to (18).

(77) A diffuser for back-lighting a liquid crystal display, which has aresin layer containing the zinc oxide-based particles produced by theprocess described in any of (27) to (36).

(78) A diffuser for back-lighting a liquid crystal display, which has aresin layer containing the zinc oxide-based particles described in anyof (50) to (58).

(79) A coating composition comprising the zinc oxide-based particlesdescribed in any of (50) to (58) and a binder component capable offorming a coating film binding the zinc oxide-based particles, theproportion of the zinc oxide-based particles being 0.1 to 99% by weightand the proportion of the binder component being 1 to 99.9% by weighteach based on the total solids content of the zinc oxide-based particlesand the binder component.

(80) A coated article comprising at least one substrate selected fromthe group consisting of a resin molded article, glass and paper and acoating film provided on the substrate which is formed of the coatingcomposition described in (79).

(81) A resin composition comprising the zinc oxide-based particlesdescribed in any of (50) to (58) and a resin capable of forming acontinuous phase having dispersed therein the zinc oxide-basedparticles, the proportion of the zinc oxide-based particles being 0.1 to99% by weight and the proportion of the resin being 1 to 99.9% by weighteach based on the total solids content of the zinc oxide-based particlesand the resin.

(82) A resin molded article obtained by molding the resin compositiondescribed in (81) into at least one shape selected from the groupconsisting of a plate, a sheet, a film, and fiber.

(83) Paper comprising pulp made into paper and having dispersed thereinthe zinc oxide-based particles described in any of (50) to (58), theproportion of the zinc oxide-based particles being 0.01 to 50% by weightbased on the pulp.

(84) A cosmetic containing 0.1% by weight or more of the zincoxide-based particles process described in any of (50) to (58).

(85) A coating composition comprising the inorganic compound particlesdescribed in any of (43) to (49) and a binder component capable offorming a coating film binding the inorganic compound particles, theproportion of the inorganic compound particles being 0.1 to 99% byweight and the proportion of the binder component being 1 to 99.9% byweight each based on the total solids content of the inorganic compoundparticles and the binder component.

(86) A coated article comprising at least one substrate selected fromthe group consisting of a resin molded article, glass and paper and acoating film provided on the substrate which is formed of the coatingcomposition described in (85).

(87) A resin composition comprising the inorganic compound particlesdescribed in any of (43) to (49) and a resin capable of forming acontinuous phase having dispersed therein the inorganic compoundparticles, the proportion of the inorganic compound particles being 0.1to 99% by weight and the proportion of the resin being 1 to 99.9% byweight each based on the total solids content of the inorganic compoundparticles and the resin.

(88) A resin molded article obtained by molding the resin compositiondescribed in (87) into at least one shape selected from the groupconsisting of a plate, a sheet, a film, and fiber.

(89) Paper comprising pulp made into paper and having dispersed thereinthe inorganic compound particles described in any of (43) to (49), theproportion of the inorganic compound particles being 0.01 to 50% byweight based on the pulp.

(90) A cosmetic containing 0.1% by weight or more of the inorganiccompound particles described in any of (43) to (49).

(91) An antimicrobial agent comprising the inorganic compound particlesdescribed in any of (43) to (49).

(92) A controlled releasing agent comprising the inorganic compoundparticles described in any of (43) to (49).

(93) An adsorbent comprising the inorganic compound particles describedin any of (43) to (49).

(94) A coating composition comprising the zinc oxide-based particlesproduced by the process described in any of (27) to (36) and a bindercomponent capable of forming a coating film binding the zinc oxide-basedparticles, the proportion of the zinc oxide-based particles being 0.1 to99% by weight and the proportion of the binder component being 1 to99.9% by weight each based on the total solids content of the zincoxide-based particles and the binder component.

(95) A coated article comprising at least one substrate selected fromthe group consisting of a resin molded article, glass and paper and acoating film provided on the substrate which is formed of the coatingcomposition described in (94).

(96) A resin composition comprising the zinc oxide-based particlesproduced by the process described in any of (27) to (36) and a resincapable of forming a continuous phase having dispersed therein the zincoxide-based particles, the proportion of the zinc oxide-based particlesbeing 0.1 to 99% by weight and the proportion of the resin being 1 to99.9% by weight each based on the total solids content of the zincoxide-based particles and the resin.

(97) A resin molded article obtained by molding the resin compositiondescribed in (96) into at least one shape selected from the groupconsisting of a plate, a sheet, a film, and fiber.

(98) Paper comprising pulp made into paper and having dispersed thereinthe zinc oxide-based particles produced by the process described in anyof (27) to (36), the proportion of the zinc oxide-based particles being0.01 to 50% by weight based on the pulp.

(99) A cosmetic containing 0.1% by weight or more of the zincoxide-based particles produced by the process described in any of (27)to (36).

(100) A coating composition comprising the inorganic compound particlesproduced by the process described in any of (19) to (26) and a bindercomponent capable of forming a coating film binding the inorganiccompound particles, the proportion of the inorganic compound particlesbeing 0.1 to 99% by weight and the proportion of the binder componentbeing 1 to 99.9% by weight each based on the total solids content of theinorganic compound particles and the binder component.

(101) A coated article comprising at least one substrate selected fromthe group consisting of a resin molded article, glass and paper and acoating film provided on the substrate which is formed of the coatingcomposition described in (100).

(102) A resin composition comprising the inorganic compound particlesproduced by the process described in any of (19) to (26) and a resincapable of forming a continuous phase having dispersed therein theinorganic compound particles, the proportion of the inorganic compoundparticles being 0.1 to 99% by weight and the proportion of the resinbeing 1 to 99.9% by weight each based on the total solids content of theinorganic compound particles and the resin.

(103) A resin molded article obtained by molding the resin compositiondescribed in (102) into at least one shape selected from the groupconsisting of a plate, a sheet, a film, and fiber.

(104) Paper comprising pulp made into paper and having dispersed thereinthe inorganic compound particles produced by the process described inany of (19) to (26), the proportion of the inorganic compound particlesbeing 0.01 to 50% by weight based on the pulp.

(105) A cosmetic containing 0.1% by weight or more of the inorganiccompound particles produced by the process described in any of (19) to(26).

(106) An antimicrobial agent comprising the inorganic compound particlesproduced by the process described in any of (19) to (26).

(107) A controlled releasing agent comprising the inorganic compoundparticles produced by the process described in any of (19) to (26).

(108) An adsorbent comprising the inorganic compound particles producedby the process described in any of (19) to (26).

(109) An adhesive comprising zinc oxide-polymer composite particlesproduced by the process described in any of (10) to (18).

(110) An adhesive comprising the zinc oxide-polymer composite particlesdescribed in any of (37) to (42).

The present invention will be described below in detail.

The process for producing zinc oxide fine particles described in (1) to(9) above is first explained.

The zinc oxide fine particles as referred to in the inventionessentially comprise zinc atoms and oxygen atoms in a proportion of 60%by weight or more in the form of ZnO and exhibit an X-ray diffractionpattern of a hexagonal system (wurtzite structure), a cubic system (rocksalt structure) or a face-centered-cubic structure. Therefore, as far asthe amount of zinc and oxygen falls within the above range, the zincoxide fine particles include composite fine particles of zinc oxidecrystals and a metal element other than zinc, e.g., an alkali metal oran alkaline earth metal, in the form of an atom or an ion; fineparticles of solid solutions of an inorganic compound of a metal elementother than zinc, e.g., an oxide, a hydroxide, a sulfide, a nitride, acarbide or a carbonate, in zinc oxide crystals; fine particles in whichan organometallic compound, such as a coupling agent (e.g., a silanecoupling agent and an alumina coupling agent), an organosiloxane or achelate compound, is bound to the surface of the zinc oxide crystals orforms a coating layer on the surface of the zinc oxide crystals; andfine particles containing a halogen element, an inorganic acid (e.g., asulfuric acid radical and a nitric acid radical) or an organic compound(e.g., a fatty acid, an alcohol, and an amine) in the inside and/or onthe surface thereof.

While the size of the zinc oxide fine particles obtained by the processof the invention is not particularly limited, zinc oxide fine particleshaving an average primary particle size controlled within a range offrom 0.005 to 10 μm, particularly of from 0.005 to 0.1 μm, andexhibiting excellent dispersibility can be produced through a simpleprocess not heretofore attempted.

The zinc oxide fine particles prepared by the process of the inventionare obtained as a dispersion containing 1 to 80% by weight, in terms ofzinc oxide, of finely divided zinc oxide particles. The zinc oxide fineparticles can be in the following state in the dispersion.

(a) Primary particles are finely dispersed without undergoing secondaryagglomeration.

(b) Primary particles are in a secondarily agglomerated state partly ortotally.

(c) Particles of different kind in which zinc oxide primary particlesare dispersed are dispersed.

All the states illustrated above are included in the concept representedby the term “dispersion” of zinc oxide fine particles.

The zinc source used as a raw material is by no means limited providedthat it is zinc or a compound containing zinc. Preferred zinc sourcesinclude metallic zinc (zinc powder), zinc oxide (zinc white), zinchydroxide, basic zinc carbonate, zinc acetate, zinc octylate, zincstearate, zinc oxalate, zinc lactate, zinc tartrate, and zincnaphthenate; for they do not require a desalting step that has beenessential in a conventional process starting with zinc chloride, zincnitrate, zinc sulfate, etc. Still preferred of them are metallic zinc(zinc powder), zinc oxide (zinc white), zinc hydroxide, basic zinccarbonate, and zinc acetate for their inexpensiveness and ease inhandling. Zinc oxide, zinc hydroxide, and zinc acetate are particularlypreferred for ease in controlling the size and shape of the resultingzinc oxide fine particles.

The carboxyl-containing compound for use in the invention includes allthe compounds containing at least one carboxyl group per molecule.Specific examples of such compounds include acyclic carboxylic acids,such as saturated fatty acids (or saturated monocarboxylic acids), e.g.,formic acid, acetic acid, propionic acid, isobutyric acid, caproic acid,caprylic acid, lauric acid, myristic acid, palmitic acid, and stearicacid; unsaturated fatty acids (or unsaturated monocarboxylic acids),e.g., acrylic acid, methacrylic acid, crotonic acid, oleic acid, andlinolenic acid; saturated polycarboxylic acids, e.g., oxalic acid,malonic acid, succinic acid, adipic acid, suberic acid, andβ,β-dimethylglutaric acid; and unsaturated polycarboxylic acids, e.g.,maleic acid and fumaric acid; cyclic saturated carboxylic acids, such ascyclohexanecarboxylic acid; aromatic carboxylic acids, such as aromaticmonocarboxylic acids, e.g., benzoic acid, phenylacetic acid, andtoluylic acid; and unsaturated polycarboxylic acids, e.g., phthalicacid, isophthalic acid, terephthalic acid, pyromellitic acid, andtrimellitic acid; carboxylic acid anhydrides, such as acetic anhydride,maleic anhydride, and pyromellitic anhydride; compounds having afunctional group or atomic group other than a carboxylic group (e.g., ahydroxyl group, an amino group, a nitro group, an alkoxy group, asulfonic acid group, a cyano group, a halogen atom, etc.) in themolecule thereof, such as trifluoroacetic acid, monochloroacetic acid,o-chlorobenzoic acid, o-nitrobenzoic acid, anthranilic acid,p-aminobenzoic acid, anisic acid (i.e., p-methoxybenzoic acid), toluylicacid, lactic acid, and salicylic acid (i.e., o-hydroxybenzoic acid); andpolymers comprising the above-described unsaturated carboxylic acid asat least one constituent unit, such as acrylic acid homopolymers andacrylic acid-methyl methacrylate copolymers. Preferred among them aresaturated fatty acids having a boiling point of 200° C. or lower atatmospheric pressure.

The carboxyl-containing compound further include carboxyl-containingzinc compounds, such as zinc carboxylates, e.g., zinc acetate and zincoxalate. When such zinc compounds are used as a zinc source, it is notalways necessary to separately add the above-mentionedcarboxyl-containing compound.

The alcohol which can be used as a raw material in the inventionincludes aliphatic monohydric alcohols, such as methanol, ethanol,isopropyl alcohol, n-butanol, t-butyl alcohol, and stearyl alcohol;aliphatic unsaturated monohydric alcohols, such as allyl alcohol, crotylalcohol, and propargyl alcohol; alicyclic monohydric alcohols, such ascyclopentanol and cyclohexanol; aromatic monohydric alcohols, such asbenzyl alcohol, cinnamyl alcohol, and methyl phenyl carbinol;heterocyclic monohydric alcohols, such as furfuryl alcohol; glycols,such as ethylene glycol, propylene glycol, trimethylene glycol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,8-octanediol,1,10-decanediol, pinacol, diethylene glycol, and triethylene glycol;aliphatic glycols having an aromatic ring, such as hydrobenzoin,benzpinacol, and phthalyl alcohol; alicyclic glycols, such ascyclopentane-1,2-diol, cyclohexane-1,2-diol, and cyclohexane-1,4-diol;polyoxyalkylene glycols (e.g., polyethylene glycol and polypropyleneglycol); and monoethers and monoesters of the above-described glycols,such as ethylene glycol monoethyl ether, ethylene glycol monobutylether, triethylene glycol monomethyl ether, and ethylene glycolmonoacetate; aromatic diols, such as hydroquinone, resorcin, and2,2-bis(4-hydroxyphenyl)propane, and monoethers and monoesters of thesediols; and trihydric alcohols, such as glycerol, and alcoholicderivatives of the trihydric alcohols, such as monoethers, monoesters,diethers, and diesters. These compounds can be used either individuallyor as a combination of two or more thereof. In particular, alcoholshaving a boiling point of 120° C. or higher at atmospheric pressure arepreferred; for fine particles of excellent crystalline properties caneasily be obtained under atmospheric pressure and in a short time. Forease of obtaining fine particles having excellent dispersibility,monohydric alcohols having a boiling point of 120° C. or higher and awater solubility of not less than 1% by weight at 20° C., for example,monoethers or monoesters of glycols and n-butanol, are especiallypreferred.

The present invention is characterized in that a mixture comprising theaforementioned zinc source, carboxyl-containing compound and alcohol isheated. The zinc source is converted to zinc oxide which is X-raycrystallographically crystalline upon being heated in a mixture of thecarboxyl-containing compound and the alcohol, and, at the same time, adispersion containing zinc oxide fine particles is obtained. If any oneof the three components, i.e., a zinc source, a carboxyl-containingcompound, and an alcohol, is missing, precipitation of zinc oxidecrystals does not take place, resulting in a failure of obtaining adispersion of zinc oxide fine particles.

The step of conversion of a zinc source to X-ray crystallographicallycrystalline zinc oxide sometimes involves formation of one or more zincoxide precursors. The case of using zinc oxide as a zinc source may bementioned as an example. In this case, the term “zinc oxide precursors”means ions or compounds other than zinc oxide which contain at least azinc atom. For example, the precursors include a zinc (hydrate) ion(Zn²⁺), a polynuclear hydroxide ion of zinc, the above ions partly ortotally chelated by a chelating compound, e.g., a β-dicarbonyl compound(e.g., acetylacetone), lactic acid, ethylene glycol or ethanolamine, anda (basic) carboxylic acid salt, such as (basic) zinc acetate, (basic)zinc salicylate, and (basic) zinc lactate. The precursor may be presentwith a part or the whole thereof forming a composite composition withthe carboxyl-containing compound and/or the alcohol as, for example, acomplex salt.

In the stage where a zinc source is converted to zinc oxide fineparticles, the carboxyl-containing compound in the mixture does notchange or partly or totally undergoes esterification with a part or thewhole of the alcohol in the mixture to form an ester compound.

The mixture is not limited provided that it is a mixture obtained bymixing the above-described three essential components, i.e., a zincsource, a carboxyl-containing compound, and an alcohol. If desired, themixture may contain components other than the three components, such aswater; organic solvents, e.g., ketones, esters, (cyclo)paraffins,ethers, and aromatic compounds; additives hereinafter described;metallic components other than zinc, e.g., inorganic metal salts (e.g.,an acetate, a nitrate or a chloride) and organometallic alkoxides (e.g.,metal alkoxides). The water or organic solvents are usually used as asolvent component.

The state of the three components in the mixture, considered eithermutually or individually, is not particularly limited. Taking the zincsource, for instance, it can be dissolved as such in a solventcomponent, such as the alcohol and/or water or an organic solvent; orthe zinc source is changed to the above-described zinc oxide precursorand dissolved or dispersed in a colloidal, emulsified or suspendedstate.

Accordingly, the state of the mixture is not particularly limited.Whether the mixture is liquid, sol, an emulsion or a suspension is of noproblem.

While the raw material composition for preparing the mixture is notparticularly limited, it is desirable from the viewpoint of economy andease of formation of zinc oxide fine particles that the amount of thezinc source to be used as a raw material of the mixture ranges from 0.1to 95% by weight, in terms of ZnO, based on the total amount of themixture and that the amount of the carboxyl-containing compound to beused as a raw material of the mixture ranges from 0.5 to 50 mol per moleof Zn atoms of the zinc source used as a raw material of the mixture.The above ranges are usually selected.

The mixture is prepared by mixing the components in the above ranges.The manner of preparation is not particularly restricted.

In order to obtain a dispersion of zinc oxide fine particles whilecontrolling the average particle size of the primary particles within arange of from 0.005 to 10 μm, it is preferred for practical productivityto add the first mixture comprising a zinc source and acarboxyl-containing compound to a heated alcohol-containing solution toprepare the second mixture.

It is particularly preferred that a first mixture is obtained from azinc source and a carboxyl-containing compound, and the first mixture isadded to an alcohol-containing solution maintained at 60° C. or above,preferably at 100° C. or higher, to prepare a second mixture, and theresulting second mixture is heated.

The method of preparing the mixture according to the above-describedpreferred mode is further illustrated below.

Addition of the first mixture can be carried out by adding the wholeamount of the first mixture all at once, or adding the first mixturedropwise on or into the alcohol-containing solution, or spraying thefirst mixture.

Addition of the first mixture may be conducted at atmospheric pressure,under pressure, or under reduced pressure. Addition at atmosphericpressure is preferred from the economical consideration. In this case,when a zinc oxide fine particle dispersion having uniformity in particlesize and shape, etc. and a controlled dispersed or agglomerated state isdesired, it is preferable to keep the alcohol-containing solution at 60°C. or higher, particularly 100° C. to 300° C., during addition andmixing. If the temperature of the alcohol-containing solution duringaddition and mixing is lower than 60° C., the viscosity of the secondmixture tends to increase suddenly during or after addition and mixing,resulting in gelation. If this happens, there arise such problems thatstirring is impossible and unsuccessfully achieves uniform mixing orheat conduction in the subsequent step, i.e., heating, is insufficient,resulting in creation of temperature distribution. It follows that zincoxide fine particles uniform in crystalline properties, particle sizeand particle shape can hardly be obtained but agglomerated particles.This problem also concerns the concentration of zinc in the secondmixture and is more liable to occur at a higher zinc concentration. Thelowest suitable temperature varies according to the pressure of thesystem. When the first mixture is added under reduced pressure or underpressure, the temperature of the alcoholic solvent should be selectedappropriately. This does not apply when a dispersion of agglomeratedzinc oxide fine particles is desired. When the first mixture is added tothe alcohol-containing solution under heating as described above, partof the carboxyl-containing compound and/or part of the alcohol of thesecond mixture are sometimes driven out of the system throughevaporation. The mixture thus prepared is also included in the conceptof “second mixture”.

While the raw material composition for preparing the first mixture isnot particularly limited, it is preferable that the amount of the zincsource to be used as a raw material of the first mixture ranges from 1to 90% by weight, in terms of ZnO, based on the total amount of thefirst mixture and that the amount of the carboxyl-containing compound tobe used as a raw material of the first mixture ranges from 0.5 to 50 molper mole of Zn atoms of the zinc source.

The thus prepared first mixture is added and mixed with thealcohol-containing solution to obtain the second mixture.

The first mixture when added may be at room temperature or as heated.For obtaining a uniform mixture, the alcohol-containing solution ispreferably stirred while the first mixture is being added thereto.

While not limiting, the amount of the alcohol in the alcohol-containingsolution preferably ranges from 1 to 100 mol per mole of the Zn atomoriginated in the zinc source present in the second mixture so that theformation of zinc oxide fine particles under heating may be completed ina short time period. The alcohol concentration in the alcohol-containingsolution is usually in a range of from 5 to 100% by weight based on thetotal weight of the solution.

Heating of the thus prepared second mixture results in production of adispersion containing zinc oxide fine particles in good yield.

The heating temperature is not particularly limited. The heating mustbe, as a matter of course, at or above the temperature at whichcrystalline zinc oxide precipitates, but the temperature cannot bedecided definitely because it is subject to variation in accordance withdesired morphology of zinc oxide fine particles, such as the size, shapeand state of dispersion or agglomeration. The heating temperature andheating time should be selected from a comprehensive point of viewincluding the initial composition of the second mixture and theabove-mentioned various parameters. In particular, when it is desired toobtain a dispersion of zinc oxide fine particles having the averageprimary particle size controlled within a range of 0.005 to 10 μm with apractical productivity, it is preferable to heat the second mixture at100° C. or higher, still preferably 100 to 300° C., particularlypreferably 120 to 200° C.

In the case when the first mixture is added to an alcohol-containingsolution kept at 100° C. or higher, heating of the resulting secondmixture can be achieved by maintaining the mixture at that temperature,or the mixture is heated or cooled to a prescribed temperature, followedby carrying out a heat treatment. In the case when the first mixture isadded to an alcohol-containing solution below 100° C. the resultingsecond mixture is heated to 100° C. or higher, followed by carrying outa heat treatment. To set the second mixture heating temperature at 100°C. or higher brings about the advantage that strict control on thecomposition of the reaction system for obtaining zinc oxide fineparticles, inclusive of control on the rate of evaporation of excessiveor unnecessary components and the amount of evaporated components, canbe taken easily. As a result, the particle size and the like of theresulting fine particles can be controlled easily.

In the heating step for obtaining the dispersion, the components otherthan the above-described ones, i.e., the alcohol, the aforesaid estercompound produced upon heating, or the solvent component which may, ifdesired, have been used in the mixture may be removed by evaporationpartially or completely.

While not limiting, a preferred heating time for completion of thereaction is usually about 0.1 to 30 hours.

Where water is present in the second mixture, it is preferable forconversion to zinc oxide fine particles to evaporate the water duringthe heating step to reduce the free water content to 5% by weight orlower, particularly 1% by weight or lower. If the water content exceedsthe above level, cases are sometimes met with that the zinc oxide fineparticles have reduced crystalline properties, resulting in a failure offulfilling the function of zinc oxide, while such depends on the kindsof the other components present in the dispersion, such as the alcohol.

It is preferable that the amount of the carboxyl-containing compound ina finally obtained zinc oxide fine particle dispersion be 0.5 mol orless per mole of the total zinc atoms present in the dispersion. If itexceeds 0.5 mol, cases are sometimes met with that the zinc oxide fineparticles have reduced crystalline properties, failing to fulfill thefunction of zinc oxide. Accordingly, where the amount of thecarboxyl-containing compound present in the second mixture is such thatthe amount of the carboxyl-containing compound in the finally obtaineddispersion will exceed 0.5 mol per mole of the total zinc atoms in theresulting dispersion, at least the excess should be removed byevaporation during the heating step. Needless to say, thecarboxyl-containing compound may be evaporated during heating even ifthe above molar ratio is 0.5 or lower.

It is also possible to add a specific additive to the system in the stepof heating for the purpose of controlling the size, shape, dispersedstate or higher-order state of the primary particles of the finallyobtained zinc oxide fine particles and/or the polarity or composition ofthe surface of the fine particles. The stage of addition of the additiveis not particularly restricted. The additive can be added in either ofthe step of preparing the second mixture or the first mixture or thestep of heating. The stage of addition is selected appropriatelyaccording to the purpose and the kind of the additive. In many cases,the effects of the additive are fully exerted when added immediatelybefore or after precipitation of zinc oxide crystals.

In particular, in order to obtain zinc oxide fine particles having highuniformity in size and shape of the primary particles, it is preferablethat a compound containing in the molecule thereof one or more than oneatomic group of at least one kind selected from the group consisting ofa carboxyl group, an amino group, a quaternary ammonio group, an amidogroup, an imido bond, a hydroxyl group, a carboxylic acid ester bond, aurethane group, a urethane bond, a ureido group, a ureylene bond, anisocyanate group, an epoxy group, a phosphoric acid group, a metallichydroxyl group, a metallic alkoxy group, and a sulfonic acid group andhaving a molecular weight of less than 1,000 be present as an additivein the system in the heating step.

Useful additives include the above-illustrated carboxyl-containingcompounds, such as long-chain saturated fatty acids (e.g., caprylicacid, lauric acid, myristic acid, palmitic acid, and stearic acid) andesters thereof; amino-containing compounds, such as alcohols having aprimary, secondary or tertiary amino group (e.g., monoethanolamine,diethanolamine, and N,N-dimethylethanolamine), quaternary ammonium salts(e.g., tetramethylammonium hydroxide and n-hexadecyltrimethylammoniumhydroxide), amino acids, amino(di)carboxylic acids and esters oranhydrides thereof (e.g., 6-aminocaproic acid,N,N-bis(octylaminoethyl)glycine, p-aminobenzoic acid, aspartic acid, andglutamic acid), pyridine derivatives (e.g., 2-hydroxypyridine andpyridine-2,6-dicarboxylic acid), and aliphatic amines (e.g.,octadecylamine and stearylamine); amides, such as dimethylformamide,dimethylacetamide, benzamide, oxamide, and oxamic acid; imino-containingcompounds, such as acid imides (e.g., succinimide and phthalimide),imino(di)carboxylic acids (e.g., imino(di)acetic acid), and iminoethers;ureido-containing compounds and derivatives thereof, such asdicarboxylic acid ureides (e.g., parabanic acid, alloxan, barbituricacid, and dialuric acid), ureido-acids (e.g., oxaluric acid andmalonuric acid), diureides (e.g., uric acid), β-aldehyde-acid ureides(e.g., uracil), and α-oxyacid ureides (e.g., 5-methylhydantoin);urethane compounds (e.g., ethyl carbamate) and derivatives thereof, suchas N-nitroso compounds and N-chloroacetylated compounds;isocyanate-containing compounds (e.g., tolylene diisocyanate,diisocyanyl diphenylmethane, hexamethylene diisocyanate, isobutylisocyanate, and phenyl isocyanate); epoxy-containing compounds, such asaliphatic diglycidyl ethers (e.g., 1,2-epoxycyclohexene, 1,8-cineole,ethylene glycol diglycidyl ether, and 1,6-hexanediol diglycidyl ether),polyglycidyl ethers (e.g., glycerol triglycidyl ether andpentaerythritol tetraglycidyl ether), aliphatic and aromatic diglycidylesters (e.g., diglycidyl adipate), resorcin glycidyl ether, bisphenol Adiglycidyl ether, and oligomers having an epoxy group as a functionalgroup; various coupling agents including silane coupling agents (e.g.,methyltrimethoxysilane, phenyltrimethoxysilane, benzyltriethoxysilane,γ-aminopropyltriethoxysilane,N-β(aminoethyl)γ-aminopropyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, andstearyltrimethoxysilane), titanate coupling agents (e.g.,isopropyltriisostearoyl titanate, bis(dioctyl pyrophosphate)oxyacetatetitanate, tetraoactylbis(ditridecyl phosphite) titanate, andisopropyltri(N-aminoethylaminoethyl) titanate), and aluminum couplingagents (e.g., ethylacetoacetatealuminum diisopropylate), and partialhydrolysis products thereof; organometallic compounds containing ametallic hydroxyl group and/or a metallic alkoxy group other than theabove-described coupling agents, such as metal alkoxides (e.g.,tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane,diethoxydimethylsilane, trimethylethoxysilane,hydroxyethyltriethoxysilane, titanium tetraethoxide, titaniumtetrabutoxide, titanium diethyldiethoxide, titanium tetrabutoxide,zirconium tetramethoxide, zirconium tetrabutoxide, aluminumtrimethoxide, aluminum tri-n-butoxide, aluminum triisopropoxide, borontriethoxide, tri-n-butyl borate, gallium triethoxide, galliumtri-n-butoxide, strontium diethoxide, tungsten hexaethoxide, manganesedi-n-butoxide, cobalt diisopropoxide, nickel diethoxide, nickeldi-n-butoxide, lanthanum triethoxide, barium diethoxide, yttriumtriethoxide, copper diethoxide, copper di-n-butoxide, niobiumpentaethoxide, niobium penta-n-butoxide, tantalum pentaethoxide,tantalum penta-n-butoxide, indium triethoxide, indium tri-n-butoxide,tin tetraethoxide, tin tetra-n-butoxide, iron triethoxide, and irontri-n-butoxide) and derivatives of these organometallic compounds, suchas (partial) hydrolysis products or condensation products (e.g.,oligomers or polymers) obtained by (partial) hydrolysis and/orcondensation of the organometallic compounds either individually or ascombined; organophosphorus compounds, such as phosphoric esters (e.g.,trimethyl phosphate, triethyl phosphate, tributyl phosphate,tris(2-chloroethyl) phosphate, and(polyoxyethylene)bis[bis(2-chloroethyl)phosphate]), acid phosphoricesters (e.g., methyl acid phosphate, propyl acid phosphate, lauryl acidphosphate, stearyl acid phosphate, bis-2-ethylhexyl phosphate, anddiisodecyl phosphate), phosphorous esters (e.g., trimethyl phosphite),and thiophosphoric esters (e.g., diisopropyl dithiophosphate);organopolysiloxanes containing in the molecule thereof at least one ofthe above-mentioned atomic groups, such as an amino group (a primary,secondary or tertiary amino group, a quaternary ammonio group, etc.), acarboxyl group, a sulfonic acid group, a phosphoric acid group, ahydroxyl group, and an epoxy group; various surface active agentscontaining the above-mentioned atomic group, such as anionic surfaceactive agents (e.g., sodium lauryl sulfate, sodiumdodecylbenzenesulfonate, sodium polyoxyethylene lauryl ether sulfate, asodium dialkylsulfosuccinate, and calcium stearate), nonionic surfaceactive agents (e.g., polyoxyethylene lauryl ether, a polyoxyethylenealkylamine, polyethylene glycol monolaurate, and glycerol monostearate),cationic surface active agents (e.g., lauryldimethylamine andstearyltrimethylammonium chloride), and amphoteric surface active agents(e.g., lauryl betaine and stearylamine acetate); and polymers containingat least one of the above-described atomic groups, such as (meth)acrylicpolymers (e.g., an acrylic acid-methyl methacrylate copolymer andacrylamide-methyl methacrylate copolymer), polyurethanes, andpolyesters.

Further, the shape or size of the crystals can be controlled by additionof a chelating agent (multidentate ligand) capable of multidentatecoordination to a zinc ion to form a chelate compound.

Examples of the chelating agent (multidentate ligand) capable of forminga chelate compound through multidentate coordination to a zinc ion areβ-diketones (e.g., acetylacetone, ethyl acetoacetate, andbenzoylacetone), ethylenediamine, dimethyl glyoxime, benzyl dioxime,cyclohexane-1,2-dione dioxime, dithizone, oxine, glycine, glycolic acid,oxalic acid, catechol, dipyridine, 1,10-phenanthroline,α-hydroxypropionic acid, monoethanolamine, diethanolamine, and ethyleneglycol.

As previously described, the resulting zinc oxide fine particles showwide variations in shape and size of the primary particles, the state ofdispersion or higher-order structure of the primary particles, surfacepolarity, surface composition, and the like depending on the kind oramount of the additive. For example, there are cases in which compositefine particles comprising the additive and zinc oxide fine particles areobtained, or zinc oxide particles unique in shape and/or higher-orderstructure of the primary particles are obtained. Taking, for instance,addition of a compound having a hydrophilic main chain, such asmethoxypoly(oxyethylene)monoglycolic acid, there are obtained zinc oxidefine particles which are regular in size and shape of the primaryparticles and also exhibit excellent dispersibility of the primaryparticles in a polar solvent, such as water. When in using a compoundhaving a highly hydrophobic or lipophilic main chain, such as analkyltrialkoxysilane or octadecylamine, there are obtained zinc oxidefine particles which are regular in size and shape of the primaryparticles and also exhibit excellent dispersibility of the primaryparticles in a low-polar or non-polar solvent, such as toluene.

While not limiting, a preferred amount of the additive to be added isusually 0.1 to 30% by weight based on the zinc oxide contained in thedispersion. If the amount is less than 0.1%, the effect of addition isinsubstantial. If it exceeds 30%, the system tends to fail to producezinc oxide.

The additives may be used either individually or as a mixture thereof.The manner of addition is not restricted and can appropriately beselected according to the kind of the additive or the time of addition.When an additive is added during heating, for example, it can be addedto the system either as such or as dissolved in and/or diluted with anarbitrary solvent, such as an alcohol. The latter manner is advantageousin that the additive is diffused through the reaction system more easilyto produce higher effects of addition.

If carbon dioxide and/or a carbonic acid source is/are present in thestep of mixing the first mixture with an alcohol-containing solution(second mixing step) or in the step of heating the resulting secondmixture, fine particles whose primary particles have regular shape andsize, excellent dispersibility in water, and very small size (0.05 μm orsmaller) can be obtained easily. Instead of using a carbonic acid sourceseparately, (basic) zinc carbonate may be used as part of a zinc sourceto serve in substitution for a carbonic acid source. A suitable amountof a carbonic acid source is 0.1 to 20 mol % based on zinc. Too muchcarbonic acid sometimes interferes with crystallization of zinc oxide,and such being the case, the heating temperature must be increased.Carbonic acid sources include, in addition to zinc carbonate, compoundsproducing carbonate ions or carbon acid gas on, e.g., heating, such asammonium carbonate, ammonium hydrogencarbonate, and urea; metalcarbonates, such as yttrium carbonate, cadmium carbonate, silvercarbonate, samarium carbonate, zirconium carbonate, cerium carbonate,thallium carbonate, lead carbonate, and bismuth carbonate; and basicmetal carbonates, such as basic zinc carbonate, basic cobalt(II)carbonate, basic copper(II) carbonate, basic lead(II) carbonate, andbasic nickel(II) carbonate. These carbonic acid sources can be usedeither individually or as a combination of two or more thereof.

As a preferred embodiment of the invention, zinc oxide fine particleshaving an average primary particle size controlled within a range offrom 0.005 to 0.1 μm can be obtained when any one of the followingconditions (I) to (IV), preferably 2 or 3 of (I) to (IV), stillpreferably all of (I) to (IV) are satisfied.

(I) Of the above-described zinc sources, a zinc source mainly comprisingat least one compound selected from the group consisting of zinc oxide,zinc hydroxide, and zinc acetate, particularly a zinc source mainlycomprising zinc oxide and/or zinc hydroxide is used.

Zinc oxide, zinc hydroxide, and zinc acetate contain substantially noimpurity that might interfere with the reaction forming zinc oxide fineparticles in the heating step, therefore making it easy to strictlycontrol the particle size to such fineness of 0.005 to 0.1 μm. Aboveall, zinc oxide and zinc hydroxide are available at a low price, allow afree choice of the carboxyl-containing compound to be combined with, andmake it particularly easy to obtain fine particles within the aboveparticle size range.

(II) The carboxyl-containing compound is a saturated fatty acid having aboiling point of 200° C. or lower at atmospheric pressure.

Specifically, formic acid, acetic acid, propionic acid, butyric acid,and isobutyric acid are preferred. With these compounds, it is easy tocontrol the carboxyl group content in the reaction system from mixingthrough heating, thus making it easy to strictly control the primaryparticle size to such fineness. It is still preferable to use the abovesaturated fatty acid in a proportion of 80 mol % or higher in the totalcarboxyl-containing compounds.

While the content of the carboxyl-containing compound falling within theabove-described preferred range is not limited further, a particularlypreferred content of the carboxyl-containing compound in the firstmixture ranges from 2.2 to 10 mol per mole of Zn atoms of the zincsource for obtaining fine particles which are prevented from secondaryagglomeration and exhibit excellent dispersibility.

(III) The second mixture is prepared by adding the first mixture,obtained by mixing zinc or a compound thereof and a carboxyl-containingcompound, kept at 60° C. or above to an alcohol-containing solution keptat 100° C. or above, particularly 100° to 300° C., by continuous orintermittent dropwise addition.

The first mixture is preferably in a liquid state. It is stillpreferable that the zinc source and the carboxyl-containing compound aremutually dissolved or they are dissolved in a solvent having highcompatibility with both of them. Water, alcohols, ketones, and estersare advantageous as such a solvent in that they easily dissolve the zincsource and the carboxyl-containing compound under heating at roomtemperature up to about 100° C. and that they are also highly compatiblewith the alcoholic solvent. The term “alcohols” as used above embracesall the alcohol species hereinabove described.

(IV) The heating of the second mixture is conducted at 100° to 300° C.,particularly 120° C. or higher.

The zinc oxide fine particles having an average primary particle sizeranging from 0.005 to 0.1 μm can be made into those having furthercontrolled uniformity in size and shape of their primary particles,controlled surface conditions, such as hydrophilic/lipophilicproperties, or a controlled state of dispersion or agglomeration.Effective methods for controlling these attributes are described below.In the preferred process for producing zinc oxide fine particles havingan average primary particle size of 0.005 to 0.1 μm, addition of theabove-described additive in the same manner as described above iseffective in obtaining zinc oxide fine particles having a controlledprimary particle shape, a controlled state of primary particledispersion or higher-order structure, controlled surface polarity, andthe like, and composite fine particles having dispersed therein suchzinc oxide fine particles. When it is desired to produce zinc oxide fineparticles having a regular primary particle size distribution, with theaverage particle size substantially falling within the above range, andhaving excellent dispersibility in various solvents, it is preferable touse a zinc source comprising at least one compound selected from thegroup consisting of zinc oxide, zinc hydroxide, and zinc acetate as amain component and, as a secondary component, basic zinc carbonateand/or a zinc salt of a carboxyl-containing compound having a boilingpoint higher than the heating temperature at atmospheric pressure. Theratio of the secondary component to the main component is 0.01 to 20% interms of zinc atom ratio. If the ratio is less than 0.01%, the effect ofthe combined use of the secondary component is insufficient. If itexceeds 20%, the system sometimes fails to produce zinc oxide.

When the above-described conditions are satisfied in the process of theinvention, there is obtained a dispersion of zinc oxide fine particlescontaining 1 to 80% by weight of zinc oxide in an alcohol and/or theabove-described ester compound and/or an organic solvent, in which theprimary particles have an average particle size of 0.005 to 0.1 μm, andthe shape, the surface condition, the state of dispersion oragglomeration, and the like of the particles are controlled.

The dispersion of the zinc oxide fine particles obtained in theinvention can be used as such. If desired, the dispersion can easily bepowdered or transformed to a coating composition containing the zincoxide fine particles or a dispersion of the zinc oxide fine particles ina different medium by solvent substitution.

Powder of zinc oxide can be obtained by separating the zinc oxide fineparticles from the dispersion in a conventional manner, such asfiltration, centrifugation or solvent evaporation, followed by dryingor, if desired, calcination. In particular, a powdering method in whichthe dispersion (or a concentrated dispersion) is evaporated to removethe solvent by means of a vacuum flash evaporator suppresses secondaryagglomeration of fine particles, which often occurs during drying, andis therefore preferred for obtaining zinc oxide powder having excellentdispersibility.

A dispersion of zinc oxide fine particles in a solvent different fromthat of the dispersion as obtained in the invention can be prepared by aknown method comprising mixing zinc oxide powder obtained by theabove-described powdering method with a desired solvent such as waterand dispersing the mixture with mechanical energy by means of a ballmill, a sand mill, an ultrasonic homogenizer, etc. A dispersion in adifferent solvent can also be prepared by mixing the dispersion asobtained in the invention with a desired solvent while heating thedispersion to evaporate part or the whole of the solvent to be replaced(solvent substitution under heating). The solvent to be substituted forthe initial one is not particularly limited and includes organicsolvents, such as alcohols, aliphatic or aromatic carboxylic acidesters, ketones, ethers, ether esters, aliphatic or aromatichydrocarbons, and halogenated hydrocarbons; water, mineral oil,vegetable oil, wax oil, silicone oil, and the like. A suitable solventcan be selected appropriately according to the end use.

In what follows, the process for producing zinc oxide-polymer compositeparticles described in (10) to (18) above and the zinc oxide-polymercomposite particles described in (37) to (42) are explained.

The zinc oxide-polymer composite particles according to the inventioncomprise zinc oxide fine particles and a polymer, the proportion of thezinc oxide fine particles being 50 to 99% by weight based on the totalweight of the composite fine particles and the polymer, and the zincoxide particles having an outer shell comprised of a mixture and/or acomposite of the zinc oxide fine particles and a polymer with the insideof the outer shell being hollow.

The composite particles of the invention preferably have a numberaverage particle size of 0.1 to 10 μm with a coefficient of particlesize variation being not more than 30%, particularly not more than 15%.

When the composite particles of the invention have a number averageparticle size of 0.1 to 10 μm with a coefficient of particle sizevariation being not more than 30%, it is preferable that the zinc oxidefine particles have a number average particle size of 0.005 to 0.1 μmand the ratio of the number average particle size of the zinc oxide fineparticles to that of the zinc oxide-polymer composite particles is{fraction (1/10)} to {fraction (1/1,000)}.

The composite particles of the invention have, for example, a sphericalshape and/or an ellipsoidal shape.

In order for the composite particles of the invention to have high lightdiffusing properties, the composite particles preferably have an outershell comprised of an aggregate of zinc oxide fine particles. Thosecomposite particles in which the inside of the outer shell is hollowexhibit further improved light diffusing properties.

The polymer contained in the composite particles have, for example, atleast one polar atomic group. The polar atomic group is selected fromthe group consisting of a carboxyl group, an amino group, a quaternaryammonio group, an amido group, an imido bond, a hydroxyl group, acarboxylic acid ester bond, a urethane group, a urethane bond, a ureidogroup, a ureylene bond, an isocyanate group, an epoxy group, aphosphoric acid group, a metallic hydroxyl group, a metallic alkoxygroup, and a sulfonic acid group.

The zinc oxide-polymer composite particles of the invention are producedby a process comprising heating a mixture of a zinc source, acarboxyl-containing compound, a polymer, and an alcohol to a temperatureof 100° C. or higher.

The above process preferably comprises a first mixing step and a secondmixing step. The first mixing step is a step in which the zinc sourceand the carboxyl-containing compound are mixed to prepare a firstmixture containing zinc and the carboxyl-containing compound. The secondmixing step is a step in which the first mixture and an alcohol aremixed to prepare a second mixture containing zinc and thecarboxyl-containing compound in the alcohol.

The first mixing step may be a step in which the zinc source isdissolved in a mixed solvent of the carboxyl-containing compound andwater.

The second mixing step may be a step in which the first mixture is addedto the medium maintained at 100° C. or higher.

The polymer which can be used in the process of the invention contains,for example, at least one polar atomic group. The polar atomic group is,for example, at least one atomic group selected from the groupconsisting of a carboxyl group, an amino group, a quaternary ammoniogroup, an amido group, an imido bond, a hydroxyl group, a carboxylicacid ester bond, a urethane group, a urethane bond, a ureido group, aureylene bond, an isocyanate group, an epoxy group, a phosphoric acidgroup, a metallic hydroxyl group, a metallic alkoxy group, and asulfonic acid group.

The zinc source for use in the process is preferably at least one zinccompound selected from the group consisting of zinc oxide, zinchydroxide, and zinc acetate.

The carboxyl-containing compound for use in the process is preferably asaturated fatty acid having a boiling point of 200° C. or lower atatmospheric pressure.

The polymer is used at a weight ratio of 0.01 to 1.0 to the zinc atoms,in terms of zinc oxide, present in the zinc source.

The zinc oxide-polymer composite particles according to the inventionare described below in greater detail.

The zinc oxide-polymer composite particles of the invention contain 50to 99% by weight, in terms of ZnO, of zinc oxide fine particles and 1 to50% by weight of a polymer, preferably 70 to 90% by weight, in terms ofZnO, of the zinc oxide fine particles and 5 to 30% by weight of thepolymer, each based on the total weight of the zinc oxide fine particlesand the polymer. If the proportion of the zinc oxide fine particles isless than the above range, there is a tendency that the UV screeningpower per composite fine particle reduces. If the proportion exceeds theupper range, the composite particles tend to have insufficientmechanical strength for practical use.

Zinc oxide that constitutes the composite particles is preferablycrystals; for crystalline zinc oxide has excellent visible lighttransmitting properties, is free from coloration, shows a wide range ofUV absorption wavelengths thereby efficiently cutting UV light, and haslow toxicity. Zinc oxide crystals generally exhibit an X-ray diffractionpattern of a hexagonal system (wurtzite structure), a cubic system (rocksalt structure) or a face-centered-cubic structure.

As far as the proportion of zinc oxide fine particles falls within theabove range, the composite particles of the invention include those inwhich a metal element other than zinc, e.g., an alkali metal or analkaline earth metal, forms, in the form of its atom or ion, a compositewith zinc oxide crystals; those in which an inorganic compound of ametal element other than zinc, e.g., an oxide, a hydroxide, a sulfide, anitride, a carbide or a carbonate, forms a solid solution in zinc oxidecrystals; those in which an organometallic compound, such as a silane,aluminum, zirconium or titanium coupling agent, an organosiloxane or achelate compound, is bound to the surface of the zinc oxide crystals orforms a coating layer on the surface of the zinc oxide crystals; andthose containing a halogen element, an inorganic acid radical (e.g., asulfuric acid radical and a nitric acid radical) or an organic compoundresidue (e.g., a fatty acid residue, an alcohol residue or an amineresidue) in the inside and/or on the surface thereof. The total weightof the zinc oxide fine particles and a polymer is preferably 75 to 100%by weight, still preferably 85 to 100% by weight. If the total weight islower than 75%, there is a tendency that the UV screening power percomposite fine particle reduces and the composite particles haveinsufficient mechanical strength for practical use.

The composite particles of the invention are not particularly limited inshape and size.

Of the composite particles of the invention, those having a numberaverage particle size of 0.1 to 10 μm, the particle size being based onthe major axis (L), with a coefficient of size variation of not morethan 30%, particularly a number average particle size of 0.1 to 2 μmwith a coefficient or size variation of not more than 15%, arepractically useful. If the number average particle size is smaller than0.1 μm, the composite particles tend to have poor dispersibility. If itexceeds 10 μm, the composite particles, when formulated into coatingcompositions, tend to have poor dispersion stability. If the coefficientof particle size distribution is more than 30%, there is a tendency thatthe composite particles have reduced dispersibility and/or dispersionstability or, when coated or molded, a coating film or the surface of amolded article becomes non-uniform.

The composite particles of the invention can have, for example, aspherical shape, an ellipsoidal shape, a cylindrical shape, a columnshape, a hexagonal prism shape, a spindle shape, a pyramidal shape or acubic shape. Spherical and/or ellipsoidal composite particles are hardlybroken by mechanical shear and are easily dispersed in coatingcompositions or resins. The term “spherical” as used herein means thatthe composite particle assumes a round shape as a whole with its L/Bratio (major axis (L)/minor axis (B)) being 1.0 or greater and smallerthan 1.2. The term “ellipsoidal” as used herein means that the compositeparticle assumes a round shape as a whole with its L/B ratio being 1.2to 5.0. Composite particles having an L/B ratio greater than 5.0 tend tohave poor dispersibility in resins or be broken by mechanical shear. Themajor axis (L) is the longest of measured three axes of the compositeparticle, and the minor axis (B) is the smaller of the width and theheight out of the three axes.

The zinc oxide fine particles may be dispersed uniformly throughout thecomposite particles or may aggregate partly and/or totally. When thezinc oxide fine particles aggregate to form an outer shell, thecomposite particles have a double layer structure in which the zincoxide fine particles are localized in the outer shell. In this case, thecomposite particles exhibit high light scattering properties because, inaddition to light scatter on the surface of the composite particles(corresponding to light scatter on conventional inorganic transparentfine particles), light are scattered on the surface of the zinc oxidefine particles within the composite particles and also on the interfacebetween the outer shell and the inner shell. In particular, when thezinc oxide fine particles constituting the composite particles have anaverage particle size of 0.005 to 0.1 μm, especially 0.005 to 0.05 μm,and the composite particles have an average particle size of 0.1 to 5μm, the composite particles exhibit high diffusing properties whilehaving high light transmitting properties. The thickness of the outershell formed by aggregation of zinc oxide fine particles is notparticularly limited but is preferably at a ratio of 0.1 to 0.4 to thenumber average particle size of the composite particles. If thethickness ratio is smaller than the above range, the composite particlestend to have reduced mechanical strength. If it exceeds the above range,the expected effects of the double layer structure may not be fullymanifested.

The zinc oxide fine particles are not particularly limited in shape andsize but must be smaller than the composite particles. For example, whenthe composite particles have a number average particle size of 0.1 to 10μm (preferably 0.1 to 2 μm), the number average particle size of thezinc oxide fine particles is 0.005 to 0.1 μm, corresponding to {fraction(1/10)} to {fraction (1/1000)} of that of the composite particles. Ifthe number average particle size of the zinc oxide fine particles issmaller than that range, the ultraviolet screening power of the zincoxide fine particles tends to be reduced. If it exceeds the above range,light transmitting properties tend to be reduced. If the ratio of thenumber average particle size of the zinc oxide fine particles to that ofthe composite particles is less than the above range, the UV screeningpower of the zinc oxide fine particles tend to be reduced. If the ratioexceeds the above range, the composite particles tend to haveinsufficient mechanical strength for practical use, or the compositeeffects tend to be exerted unsuccessfully.

Where the zinc oxide fine particles aggregate to form an outer shell,the polymer can be present only in the outer shell or the inner shell orboth of them. It is preferable that the polymer be present only in theouter shell so that the composite particles are hollow. Hollow compositeparticles have an improved light diffusing function. In particular,hollow composite particles having an average particle size of 0.1 to 5μm in which the zinc oxide fine particles have an average particle sizeof 0.005 to 0.1 μm, particularly 0.005 to 0.05 μm, have high lighttransmitting properties and extremely high light diffusing propertiesand are therefore useful as particles of a diffuser for back-lightingliquid crystal displays as hereinafter described. Where the polymer ispresent in the outer shell, covering the surface of the compositeparticles, such composite particles have excellent dispersibility and,when formulated into a resin composition, exhibit increased adhesion toa matrix polymer. Where the composite particles have many intersticesamong zinc oxide fine particles, and also where the composite particlesare hollow, such composite particles perform functions as porousparticles or microcapsules. That is, they have functions of adsorption,separation, removal, and collection, such as oil absorptivity,hygroscopicity, harmful metal ion adsorptivity, harmful gas and badorder absorptivity; heat and sound insulating functions (e.g., heatinsulating fillers or sound insulating fillers); a function ofimmobilizing metal ions, enzymes or bacteria (e.g., catalytic carriersand fillers for chromatography); light weight properties; and a functionof slowly releasing a liquid or perfume held therein.

The polymer to be used in the composite particles of the invention isnot particularly limited and can be, for example, polymers having aweight average molecular weight of 1000 to 1,000,000, including thosegenerally called oligomers or prepolymers. Since such polymers areeasily dissolved or easily emulsified or suspended as finely as possiblein the first or second mixture or in the heating system forprecipitating the composite particles, composite particles regular insize (a coefficient of particle size variation of not more than 30%) andshape can be obtained easily. The polymer to be used in the compositeparticles can be at least one resin selected from the following groups(a) to (n). When these resins are used, composite particles having anaverage particle size of 0.1 to 10 μm are obtained easily.

(a) Acrylic Resin Polymers

(1) Thermoplastic acrylic resins, for example, homo- or copolymers of(meth)acrylic monomers, such as acrylic esters and methacrylic esters;copolymers of the above-described (meth)acrylic monomers and otherpolymerizable monomers having no functional group, such as maleicesters, itaconic esters, vinyl monomers (e.g., styrene, p-chlorostyrene,vinyltoluene, vinyl acetate, vinyl chloride, vinyl methyl ether, andvinyl butyral), olefins (e.g., ethylene and propylene), dienes (e.g.,butadiene), and trienes; and modified resins or derivatives (e.g., withsubstituents introduced) of these acrylic resins and (2) thermosettingacrylic resins, such as copolymers of the above-described (meth)acrylicmonomers and other polymerizable monomers having a functional group,such as acrylic acid, methacrylic acid, acrylamide, methacrylamide,acrylonitrile, methacrylonitrile, hydroxyalkyl esters of (meth)acrylicacid, glycidyl (meth)acrylate, and aminoalkyl esters of (meth)acrylicacid; copolymers of the above-described polymerizable monomers having afunctional group, the above-described (meth)acrylic monomers, and theabove-described polymerizable monomers having no functional group, andmodified resins or derivatives (e.g., with substituents introduced, orwith the functional group neutralized) of these acrylic resins.

(b) Alkyl Resin Polymers

Polycondensates (oil-free alkyl resins) obtained from polybasic acids(e.g., phthalic anhydride, isophthalic acid, terephthalic acid, benzoicacid, rosin, adipic acid, maleic anhydride, succinic acid, sebacic acid,fumaric anhydride, trimellitic acid, and pyromellitic acid) andpolyhydric alcohols (e.g., ethylene glycol, propylene glycol, neopentylglycol, 1,6-hexanediol, glycerol, trimethylolethane, pentaerythritol,diethylene glycol, dipropylene glycol, triethylene glycol, polyethyleneglycol, polypropylene glycol, and hydrogenated bisphenol A); modifiedalkyd resins obtained by modifying the above-described polycondensateswith fats and oils (e.g., fatty acids); modified alkyd resins obtainedby modifying the above-described polycondensates or modified alkydresins with natural resins (e.g., rosin), synthetic resins (e.g.,phenolic resins, epoxy resins, urethane resins, silicone resins, andamino resins) or the monomers described in (a) above, such asrosin-modified alkyd resins, phenol-modified alkyd resins,epoxy-modified alkyd resins, styrenated alkyl resins, acryl-modifiedalkyl resins, urethane-modified alkyd resins, silicone-modified alkydresins, and amino resin-modified alkyd resins; and derivatives of theabove-described polycondensates, alkyd resins or modified alkyd resins,such as those having part or the whole of the functional group thereof(e.g., a carboxyl group) neutralized, or with a substituent introduced.

(c) Amino Resin Polymers

Melamine resins, such as melamine-formaldehyde resins, butylatedmelamine resins, methylated melamine resins, and benzoguanamine resins;urea resins, such as urea-formaldehyde resins, butylated urea resins,and butylated urea-melamine resins; amino resin-modified alkyd resinsobtained by modifying the alkyd resins described in (b) above withmelamine resins or urea resins through co-condensation reaction; andmodified resins of the above-described melamine resins, urea resins oramino resin-modified alkyd resins, such as methylated methylolmelamine,an adduct of an initial condensate of methylolmelamine and a polyhydricalcohol, condensates between melamine or urea and a polyamine, butylatedmelamine having introduced therein a hydrophilic group, and amino resinsusing benzoguanamine having introduced therein a hydrophilic group.

(d) Vinyl Resin Polymers

Homo- and copolymers of vinyl monomers (e.g., vinyl chloride, vinylacetate, vinyl propionate, vinylidene chloride, vinyl butyral, styrene,p-chlorostyrene, and vinyltoluene), such as polyvinyl chloride, vinylchloride-vinyl acetate copolymers, polyvinyl acetate, ethylene-vinylacetate copolymers, modified ethylene-vinyl acetate copolymers,polyvinyl butyral, polyvinyl alcohol, and polystyrene; copolymers of thevinyl monomers and other unsaturated monomers, such as olefins (e.g.,ethylene and propylene), dienes (e.g., butadiene), and trienes;copolymers of the vinyl monomers and the above-described (meth)acrylicmonomers and/or other unsaturated monomers; and derivatives of thesecopolymers.

(e) Epoxy Resin Polymers

Glycidyl ether epoxy resins, such as bisphenol A epoxy resins, phenoxyresins (high-molecular weight (≧30,000) bisphenol A epoxy resins),phenol novolak epoxy resins, o-cresol novolak epoxy resins, bisphenol Anovolak epoxy resins, brominated phenol novolak epoxy resins, andtetraphenylolethane epoxy resins; glycidyl ester epoxy resins;glycidylamine epoxy resins; epoxidized polybutadiene; and polymersobtained by reacting these epoxy resins with compounds having activehydrogen capable of crosslinking with an epoxy group (e.g., an aminogroup, a carboxyl group, an amido group or a thiol group) and/or(pre)polymers thereof (e.g., aliphatic (poly)amines, aromatic(poly)amines, diethylaminopropylamine, alicyclic amines, andpolymercaptan).

(f) Polyamide Resin Polymers

Nylon resins obtained by polycondensation of diamines and dicarboxylicacids (e.g., nylon 66), nylon resins obtained by ring-openingpolymerization of lactams (e.g., nylon 6), polypeptides obtained bypolycondensation of amino acids (e.g., polyglycine andpoly(α-L-alanine)), and amide derivatives of polyamines, which mayretain an amino group, obtained by dehydrating condensation ofpolycarboxylic acids (typified by polymerized fatty acids (dimer acids)which are polymers of vegetable fat and oil fatty acids) and polyamines(e.g., ethylenediamine and diethylenepolyamine).

(g) Polyimide Resin Polymers

Polyimide polymers obtained by polycondensation of tetracarboxylic aciddianhydrides (e.g., pyromellitic anhydride) and aromatic diamines,Diels-Alder polymerization of bismaleimides (e.g.,bishexamethylenemaleimide) and biscyclopentadienyl compounds or2,5-dimethyl-3,4-diphenylcyclopentadienone, etc., or the like reaction.

(h) p-Polyurethane Resin Polymers

Resins having a urethane bond in the molecule thereof, such as alkydresins with the dibasic acid thereof being substituted with adiisocyanate; polymers obtained by reacting an acrylic polymercomprising a monomer containing a hydroxyl-containing (meth)acrylicmonomer (e.g., methacrylic acid hydroxy-ester) and an isocyanatecompound; polymers obtained by reacting a polyester polymer comprising adibasic acid and an excess polyvalent alcohol and an isocyanatecompound; polymers obtained by reacting a polyalkylene glycol (obtainedby addition polymerization of a polyhydric alcohol and propylene oxideor ethylene oxide) with an isocyanate compound; polymers obtained byreacting a hydroxyl-containing epoxy resin with an isocyanate compound;polyurethane resins conventionally used in coatings, such asmoisture-curing polyurethane reins, heat-curing polyurethane resins, andcatalytic curing polyurethane resins; prepolymers having a urethane bondand a polymerizable double bond, such as phenyl glycidyl etheracrylate-hexamethylene diisocyanate urethane prepolymer, phenyl glycidylether acrylate-isophorone diisocyanate urethane prepolymer, phenylglycidyl ether acrylate-tolylene diisocyanate urethane prepolymer,glycerol dimethacrylate-hexamethylene diisocyanate urethane prepolymer,glycerol dimethacrylate-isophorone diisocyanate urethane prepolymer,pentaerythritol triacrylate-hexamethylene diisocyanate urethaneprepolymer, pentaerythritol triacrylate-isophorone diisocyanate urethaneprepolymer, and pentaerythritol triacrylate-tolylene diisocyanateurethane prepolymer; homo- or copolymers of these prepolymers;copolymers of these prepolymers and other polymerizable monomers, suchas (meth)acrylic monomers (e.g., (meth)acrylic acid, (meth)acrylicesters, (meth)acrylonitrile, and (meth)acrylamide), maleic acid, maleicesters, styrene monomers (styrene, p-chlorostyrene, and vinyltoluene),olefins (e.g., ethylene and propylene), dienes (e.g., butadiene),trienes, and vinyl monomers (e.g., vinyl acetate, vinyl chloride, vinylmethyl ether, vinyl alcohol, and vinyl butyral); and urethane acrylatepolymers obtained by reacting polyisocyanate (e.g., hexamethylenediisocyanate and toluylene diisocyanate) and (meth)acrylic acid or(meth)acrylic acid oligomers.

(i) Polyester resin polymers

Saturated or unsaturated polyester polymers obtained by polycondensationbetween at least one glycol selected from the group consisting ofaliphatic glycols (e.g., ethylene glycol, diethylene glycol, propyleneglycol, dipropylene glycol, 1,3-butanediol, 1,6-hexanediol, andneopentyl glycol), aromatic diols (e.g., hydroquinone and resorcin), andpolyalkylene glycols (e.g., polyethylene glycol and polypropyleneglycol), etc. and at least one dicarboxylic acid selected from the groupconsisting of aromatic dicarboxylic acids (e.g., phthalic acid(anhydride), isophthalic acid, terephthalic acid, andnaphthalenedicarboxylic acid), aliphatic dicarboxylic acids (e.g.,adipic acid and sebacic acid), alicyclic dicarboxylic acids (e.g.,cyclohexane-1,4-dicarboxylic acid), and unsaturated dicarboxylic acids(e.g., maleic acid (anhydride) and fumaric acid), etc.; and polymersobtained by polymerization of an unsaturated polyester with apolymerizable monomer (e.g., styrene and (meth)acrylic esters).

(j) Phenolic Resin Polymers

Phenolic resins generally termed novolak type or resol type, which areobtained by polycondensation between phenols (e.g., phenol, analkyl-substituted phenol, an allyl-substituted phenol, and bisphenol A)and formaldehyde; and derivatives thereof obtained by modification orsubstitution.

(k) Organopolysiloxane Polymers

Polymers comprising a siloxane skeleton and containing acarbon-containing organic group (e.g., an alkyl group) directly bondedto the silicon atom of the siloxane bond, such as polyalkylsiloxanes(e.g., dimethylpolysiloxane and methylphenylpolysiloxane); and theabove-described polymers with part of the organic group bonded to thesilicon atom via an oxygen atom or part of the organic group modified(modified silicone) (e.g., alkyd-modified silicone, epoxy-modifiedsilicone, polyester-modified silicone, acryl-modified silicone, andurethane-modified silicon).

(l) Acrylic Silicone Resin Polymers

Polymers obtained by copolymerizing organosilicon compounds having apolymerizable double bond (e.g., methacryloxypropyltrimethoxysilane andvinyltrimethoxysilane) and unsaturated monomers (e.g., acrylicmonomers), such as acrylic copolymers containing an alkoxysilyl group.

(m) Fluorine Resin Polymers

Homo- or copolymers of fluorine-containing polymerizable monomers, suchas ethylene fluoride, vinylidene fluoride, and vinyl fluoride; andcopolymers comprising the fluorine-containing polymerizable monomers andother polymerizable monomers, such as vinyl monomers, olefins, andacrylic monomers.

(n) Other Resin Polymers

Conventional resins, such as xylene resins, petroleum resins, ketoneresins, liquid polybutadiene, rosin-modified maleic acid resins, andcoumarone resins; and derivatives of these resins.

Preferred polymers are those having at least one polar atomic group forthe reason that the composite fine particles containing such polymersare excellent in chemical stability (solvent resistance and chemicalresistance) and mechanical characteristics. Preferred polar atomicgroups can be at least one group selected from the group consisting of acarboxyl group, an amino group (inclusive of a primary amino group, asecondary amino group, a tertiary amino group, an imino group, and animino bond), a quaternary ammonio group, an amido group, an imido bond,a hydroxyl group (alcoholic or phenolic), a carboxylic acid ester bond,a urethane group, a urethane bond, a ureido group, a ureylene bond, anisocyanate group, an epoxy group, a phosphoric acid group, a metallichydroxyl group, a metallic alkoxy group, and a sulfonic acid group. Useof the polymers containing these polar groups brings about the followingadvantages: the resulting composite particles have further improvedchemical stability and excellent mechanical strength, such as crushstrength; fine zinc oxide particles having an average particle size of0.005 to 0.1 μm can easily be obtained; and the composite particleshaving uniform particle size (coefficient of particle size distributionof not more than 30%) and uniform shape can easily be obtained.

Polymers having one or more carboxyl groups include homo- or copolymersof carboxyl-containing polymerizable monomers, such as (meth)acrylicacid, 2-(meth)acryloyloxyethylsuccinic acid,2-(meth)acryloyloxyethylphthalic acid,2-acryloyloxyethylhexahydrophthalic acid, and maleic acid; copolymers ofthe above-described carboxyl-containing polymerizable monomers and otherpolymerizable monomers, such as (meth)acrylic monomers (e.g.,(meth)acrylic esters, (meth)acrylamide, and (meth)acrylonitrile),substituted (meth)acrylic monomers (e.g., methyl α-chloromethacrylate),maleic esters, styrene monomers (e.g., styrene, p-chlorostyrene, andvinyltoluene), olefins (e.g., ethylene and propylene), dienes (e.g.,butadiene), trienes, vinyl monomers (e.g., vinyl acetate, vinylchloride, vinyl methyl ether, vinyl butyral, and vinyl alcohol), andpolymerizable organosilicon compounds (e.g., vinyltrimethoxysilane andmethacryloxytrimethoxysilane); polymers having a carboxyl group at theterminal or side chain thereof, selected from the above-described alkydresin polymers and polyester resin polymers; and carboxyl-modifiedorganopolysiloxane polymers containing a carboxyl group at the terminaland/or side chain thereof, such as dimethylpolysiloxane having acarboxypropyl group at the terminal or side chain thereof.

The polymers having one or more amino groups and/or quaternary ammoniogroups are polymers having at least one group selected from the groupconsisting of a primary amino group, a secondary amino group, a tertiaryamino group, an imino group, an imino bond, and a quaternary ammoniogroup. Examples of such polymers include homo- or copolymers of amino-,imino- or ammonio-containing polymerizable monomers, such asdimethylaminoethyl methacrylate, diethylaminoethyl methacrylate,4-vinylpyridine, p-aminostyrene, 3-vinylaniline, 4-vinylimidazole,vinylpyrrole, and dimethyldiallylammonium chloride; copolymers of theabove-described monomers and other polymerizable monomers, such as(meth)acrylic monomers (e.g., (meth)acrylic acid, (meth)acrylic esters,(meth)acrylamide, and (meth)acrylonitrile), substituted (meth)acrylicmonomers (e.g., methyl α-chloromethacrylate), maleic acid, maleicesters, styrene monomers (e.g., styrene, p-chlorostyrene, arLdvinyltoluene), olefins (e.g., ethylene and propylene), dienes (e.g.,butadiene), trienes, vinyl monomers (e.g., vinyl acetate, vinylchloride, vinyl methyl ether, vinyl butyral, and vinyl alcohol), andpolymerizable organosilicon compounds (e.g., vinyltrimethoxysilane andmethacryloxytrimethoxysilane); amino-containing polymers selected fromthe above-described polyamide resin polymers; the above-described aminoresin polymers; amino-modified organopolysilane polymers having an aminogroup at the terminal and/or side chain thereof, such asdimethylpolysiloxane having a dimethylamino group or an aminopropylgroup at the terminal or side chain thereof; alkyleneimine polymers,such as polyethyleneimine and polypropyleneimine; polymers ofpyrrolidine, piperidine, etc.; halogenated polydiallylammonium; ionenecompounds; chitosan; and porphines, such as tetramethylporphine andtetraphenylporphine.

The polymers having one or more amido groups include homo- or copolymersof amido-containing polymerizable monomers, such as (meth)acrylamide and2-acrylamido-2-methylpropanesulfonic acid; copolymers of these monomersand other polymerizable monomers, such as (meth)acrylic monomers (e.g.,(meth)acrylic acid, (meth)acrylic esters, and (meth)acrylonitrile),substituted (meth)acrylic monomers (e.g., methyl α-chloromethacrylate),maleic acid, maleic esters, styrene monomers (e.g., styrene,p-chlorostyrene, and vinyltoluene), olefins (e.g., ethylene andpropylene), dienes (e.g., butadiene), trienes, vinyl monomers (e.g.,vinyl acetate, vinyl chloride, vinyl methyl ether, vinyl butyral, andvinyl alcohol), and polymerizable organosilicon compounds (e.g.,vinyltrimethoxysilane and methacryloxytrimethoxyhsilane); theabove-described polyamide resin polymers; and amido-modifiedorganopolysiloxane polymers having an amido group at the terminal and/orside chain thereof.

The polymers having one or more imido bonds include the above-describedpolyimide resin polymers.

The polymers having one or more alcoholic hydroxyl groups include homo-or copolymers of hydroxyl-containing polymerizable monomers, such as2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, glycerol dimethacrylate, glycerolmonomethacrylate, 3-chloro-2-hydroxypropyl methacrylate,2-acryloyloxyethyl-2-hydroxyethylphthalic acid, pentaerythritoltriacrylate, 2-hydroxy-3-phenoxypropyl acrylate, bisphenolA-diepoxy-(meth)acrylic acid adducts, and vinyl alcohol; copolymers ofthese monomers and other polymerizable monomers, such as (meth)acrylicmonomers (e.g., (meth)acrylic acid, (meth)acrylic esters,(meth)acrylonitrile, and (meth)acrylamide), substituted (meth)acrylicmonomers (e.g., methyl α-chloromethacrylate), maleic acid, maleicesters, styrene monomers (e.g., styrene, p-chlorostyrene, andvinyltoluene), olefins (e.g., ethylene and propylene), dienes (e.g.,butadiene), trienes, vinyl monomers (e.g., vinyl acetate, vinylchloride, vinyl methyl ether, and vinyl butyral), and polymerizableorganosilicon compounds (e.g., vinyltrimethoxysilane andmethacryloxytrimethoxysilane); cellulose polymers, such as hydroxypropylcellulose, methyl cellulose, and hydroxyethylmethyl cellulose; polyamideresin polymers obtained by condensation of polybasic acids, such asaliphatic dicarboxylic acids, and polyamines; and organopolysiloxanepolymers containing an alcoholic hydroxyl group at the terminal and/orside chain thereof, such as dimethylpolysiloxane orpolydimethyl-hydroxyalkylene oxide methylsiloxane having carbinol orhydroxypropyl at the terminal thereof.

The polymers having one or more phenolic hydroxyl groups include theabove-described phenolic resin polymers.

The polymers having one or more carboxylic acid ester bonds includehomo- or copolymers of carboxylic acid ester-containing polymerizablemonomers, such as (meth)acrylic esters (e.g., methyl methacrylate, ethylmethacrylate, butyl methacrylate, isobutyl methacrylate, isoamylacrylate, 2-ethylhexyl methacrylate, isodecyl methacrylate, n-lauryl(meth)acrylate, benzyl acrylate, tridecyl methacrylate, n-stearyl(meth)acrylate, isooctyl acrylate, isostearyl methacrylate, behenylmethacrylate, butoxyethyl acrylate, methoxydiethylene glycolmethacrylate, n-butoxyethyl methacrylate, 2-phenoxyethyl (meth)acrylate,methoxydiethylene glycol acrylate, methoxypolyethylene glycolmethacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl(meth)acrylate, isobornyl (meth)acrylate, benzyl methacrylate, ethyleneglycol dimethacrylate, diethylene glycol dimethacrylate, 1,4-butanedioldimethacrylate, 1,6-hexanediol dimethacrylate, trimethylolpropanetri(meth)acrylate, glycerol dimethacrylate, trifluoroethyl methacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,dipentaerythritol hexaacrylate, neopentyl glycol acrylbenzoate,3-acryloyloxyglycerol monomethacrylate propylene oxide-modifiedbisphenol A diacrylate, hydrogenated dicyclopentadienyl diacrylate, andperfluorooctylethyl acrylate), maleic esters (e.g., methyl maleate andbutyl maleate), vinyl acetate, and methacryloxypropyltrimethoxysilane;copolymers of these monomers and other polymerizable monomers, such as(meth)acrylic monomers (e.g., (meth)acrylic acid, (meth)acrylonitrile,and (meth)acrylamide), maleic acid, styrene monomers (e.g., styrene,p-chlorostyrene, and vinyltoluene), olefins (e.g., ethylene andpropylene), dienes (e.g., butadiene), trienes, vinyl monomers (e.g.,vinyl chloride, vinyl methyl ether, vinyl alcohol, and vinyl butyral),and polymerizable organosilicon compounds (e.g., vinyltrimethoxysilane);the above-described polyester resin polymers; and organopolysiloxanepolymers containing an ester bond at the terminal and/or side chainthereof, such as dimethylpolysiloxane having an acetoxy group, astearyloxy group, etc. at the terminal thereof.

The polymers having one or more urethane groups and/or urethane bondsinclude the above-described polyurethane resin polymers.

The polymers having one or more ureido groups and/or ureylene bondsinclude polyurea obtained by polycondensation of nonamethylenediamineand urea.

The polymers having one or more isocyanate groups includepolymethylenepolyphenyl polyisocyanate; polyol-modified isocyanates; andpolymers obtained by reacting a polyfunctional aromatic or aliphaticisocyanate compound (e.g., hexamethylene diisocyanate or toluylenediisocyanate) with a (pre)polymer containing a functional group havingactive hydrogen (e.g., a amino group, a carboxyl group or a hydroxylgroup) (reaction between part of the isocyanate groups contained in theisocyanate compound with the functional group having active hydrogen).

The polymers having one or more epoxy groups include homo- or copolymersof epoxy-containing polymerizable monomers, such as epoxy-containing(meth)acrylic monomers (e.g., glycidyl methacrylate,N-[4-(2,3-epoxypropoxy)-3,5-dimethylbenzyl]acrylamide); copolymers ofthese monomers and other polymerizable monomers which are inert to theepoxy group during polymerization, such as (meth)acrylic monomers (e.g.,(meth)acrylic esters), substituted (meth)acrylic monomers (e.g., methylα-chloromethacrylate), maleic esters, styrene monomers (e.g., styrene,p-chlorostyrene, and vinyltoluene), olefins (e.g., ethylene andpropylene), dienes (e.g., butadiene), trienes, vinyl monomers (e.g.,vinyl acetate, vinyl chloride, vinyl methyl ether, vinyl butyral, andvinyl alcohol), and polymerizable organosilicon compounds (e.g.,vinyltrimethoxysilane and methacryloxytrimethoxysilane); theabove-described epoxy resin polymers; and organopolysiloxane polymerscontaining a glycidoxy group at the terminal and/or side chain thereof,such as polydimethylsiloxane, polyglycidoxypropylmethylsiloxane, andpolyglycidoxypropylmethyl-dimethylsiloxane copolymer having aglycidoxypropyl group at the terminal thereof.

The polymers having one or more phosphoric acid groups include homo- orcopolymers of phospho-containing polymerizable monomers, such asmono(2-methacryloyloxyethyl) acid phosphate, mono(2-acryloyloxyethyl)acid phosphate, and 2-acryloyloxyethyl acid phosphate; and copolymers ofthese monomers and other polymerizable monomers, such as (meth)acrylicmonomers (e.g., (meth)acrylic acid, (meth)acrylic esters,(meth)acrylonitrile, and (meth)acrylamide), substituted (meth)acrylicmonomers (e.g., methyl α-chloromethacrylate), maleic acid, maleicesters, styrene monomers (e.g., styrene, p-chlorostyrene, andvinyltoluene), olefins (e.g., ethylene and propylene), dienes (e.g.,butadiene), trienes, vinyl monomers (e.g., vinyl acetate, vinylchloride, vinyl methyl ether, vinyl alcohol, and vinyl butyral), andpolymerizable organosilicon compounds (e.g., vinyltrimethoxysilane andmethacryloxytrimethoxysi lane).

The polymers having one or more metallic hydroxyl groups and/or metallicalkoxy groups include copolymers of a silicon compound having apolymerizable double bond, such as methacryloxypropyltrimethoxysilane,and other polymerizable monomers, such as (meth)acrylic monomers (e.g.,(meth)acrylic acid, (meth)acrylic esters, (meth)acrylonitrile, and(meth)acrylamide), substituted (meth)acrylic monomers (e.g., methylα-chloromethacrylate), maleic acid, maleic esters, styrene monomers(e.g., styrene, p-chlorostyrene, and vinyltoluene), olefins (e.g.,ethylene and propylene), dienes (e.g., butadiene), trienes, vinylmonomers (e.g., vinyl acetate, vinyl chloride, and vinyl methyl ether),and polymerizable organosilicon compounds (e.g., vinyltrimethoxysilaneand methacryloxytrimethoxysilane); polymers obtained by (partially)hydrolyzing the alkoxysilyl group of the above-described copolymers;silanol-containing organopolysiloxanes, such as silanol-terminatedpolydimethylsiloxane, silanol-terminated polydiphenylsiloxane, andsilanol-terminated polydimethyldiphenylsiloxane orpolytetramethyl-p-silphenylenesiloxane;(N-trimethoxysilylpropyl)polyethyleneimine,(N-trimethoxysilylpropyl)-o-polyethylene oxide urethane,triethoxysilyl-modified poly(1,2-butadiene), and these polymers with thealkoxysilyl group thereof being partially hydrolyzed; and theabove-described acrylic silicone resin polymers.

The polymers having one or more sulfonic acid groups include homo- orcopolymers of sulfo-containing polymerizable monomers, such asacrylamidomethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonicacid, and a sodium salt thereof; copolymers of these monomers and otherpolymerizable monomers, such as (meth)acrylic monomers (e.g.,(meth)acrylic acid, (meth)acrylic esters, (meth)acrylonitrile, and(meth)acrylamide), substituted (meth)acrylic monomers (e.g., methylα-chloromethacrylate), maleic acid, maleic esters, styrene monomers(e.g., styrene, p-chlorostyrene, and vinyltoluene), olefins (e.g.,ethylene and propylene), dienes (e.g., butadiene), trienes, vinylmonomers (e.g., vinyl acetate, vinyl chloride, vinyl methyl ether, vinylalcohol, and vinyl butyral), and polymerizable organosilicon compounds(e.g., vinyltrimethoxysilane and methacryloxytrimethoxysilane); andsulfo-containing polymers obtained by reacting styrene polymers with asulfonating agent, e.g., concentrated sulfuric acid, chlorosulfonic acidor sulfuric anhydride.

The polymers having other polar atomic groups include ring-openedcompounds of cyclic iminoethers (e.g., (2-)substituted oxazoline and/or(2-substituted)oxazine), such as poly-N-formylethyleneimine orpoly-N-acetylethyleneimine which is obtained by ring-openingpolymerization of oxazoline or 2-methyloxazoline; polymers obtained byadsorptive coordination of metallic ions to part or all of the ligands(functional groups) of polymers having such a structure as is used inchelate resins, i.e., polymers (amongst polymers having at least onefunctional group) having a ligand (functional group) to which a metallicion can coordinate (e.g., polyvinyl alcohol, polyvinyltriacrylmethane,polyvinylmethacryloylacetone, poly(4-hydroxystyrene),pyrogallolphenol-formaldehyde resin, salicylic acid-formaldehyde resin,polyvinylsalicylic acid, polyacrylic acid, polymethacrylic acid,polyitaconic acid, aminophenol-formaldehyde resin,poly(8-hydroxy-5-vinylquinoline), polyvinylamine, polyethyleneimine,poly(4-aminostyrene), poly(3-vinylaniline), poly(4-vinylpyridine),poly(4-vinylbipyridine), poly(4-vinylimidazole), polyvinylpyrrole,polyglycine, and poly(α-L-alanine)), for example, ring-openingcopolymers obtained from cyclic iminoethers and lactones, such as anoxazoline-β-propiolactone alternating copolymer); and polymers having acarboxyl group, a sulfonic acid group, etc. in the form of its salt witha metal, e.g., an alkali metal (e.g., sodium or potassium) or analkaline earth metal (e.g., magnesium or calcium).

Of the polymers illustrated in (a) through (n), those having at leastone main chain selected from the group consisting of a (meth)acrylicunit, a styrene unit, a vinyl unit or combinations of these units, analkyd chain, a polyester chain, and a polyamide chain and at least onepolar atomic group selected from the group consisting of a carboxylgroup, an amino group, an amido group, a silanol group, and analkoxysilyl group are preferred for ease of obtaining double-layered,hollow, and spherical composite fine particles. The amount of thepolymer to be used, the equivalent amount of the polar atomic group, andthe composition of the reaction system for the formation of thecomposite fine particles (e.g., the composition of the solvent) shouldbe selected appropriately in accordance with the kind of the polymer.

The composite particles of the invention are not limited in manner ofuse as long as the temperature of use is below the thermal decompositionpoint of the polymer constituting the composite particles. For example,the composite particles can not only be compounded into those resinswhich are molded at high temperatures, such as polyesters andpolycarbonates, but can be applied to the surface of glass with the aidof an inorganic binder to form a coating film, which can then be heatedat a high temperature.

The process for producing the zinc oxide-polymer composite particles ofthe invention will further be illustrated in more detail.

While the process for producing the composite particles of the inventionis not particularly restricted, the process hereinafter described (i.e.,the process of the invention) achieves high productivity.

According to the process of the invention, a mixture comprising a zincsource, a carboxyl-containing compound, a polymer, and analcohol-containing solution is kept at a temperature of 100° C. orhigher to thereby precipitate zinc oxide-polymer composite particlescontaining zinc oxide fine particles and the polymer.

Useful zinc sources and preferred examples thereof can be thosepreviously described with respect to the process for producing zincoxide fine particles as described in (1) to (9) above. Particularlypreferred amongst them are zinc oxide and/or zinc hydroxide because oftheir availability at low prices and freedom of choice of thecarboxyl-containing compound to be combined with.

The amount of the zinc source to be used is usually 0.1 to 95% byweight, preferably 0.5 to 50% by weight, still preferably 1 to 30% byweight, in terms of ZnO, based on the total charged amount of the zincsource, the carboxyl-containing compound, and the alcohol. If the zincsource is less than the above range, the productivity tends to decrease.If it is more than the above range, the composite particles tend toundergo secondary agglomeration, hardly providing finely dispersedcomposite particles with a regular particle size distribution.

Useful carboxyl-containing compounds and preferred examples thereof canbe those previously described with respect to the process for producingzinc oxide fine particles as described in (1) to (9) above.Monocarboxylic acids are particularly preferred.

The monocarboxylic acids for use in the invention are compoundscontaining one carboxyl group per molecule. Specific examples of suchcompounds include saturated fatty acids (or saturated monocarboxylicacids), e.g., formic acid, acetic acid, propionic acid, isobutyric acid,caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid,and stearic acid; unsaturated fatty acids (or unsaturated monocarboxylicacids), e.g., acrylic acid, methacrylic acid, crotonic acid, oleic acid,and linolenic acid; cyclic saturated monocarboxylic acids, such ascyclohexanecarboxylic acid; aromatic monocarboxylic acids, e.g., benzoicacid, phenylacetic acid, and toluylic acid; anhydrides of thesemonocarboxylic acids, such as acetic anhydride; and halogen-containingmonocarboxylic acids, such as trifluoroacetic acid, monochloroaceticacid, and o-chlorobenzoic acid. These compounds can be used eitherindividually or as a combination of two or more thereof.

Preferred of the above monocarboxylic acids are saturated fatty acidshaving a boiling point of 200° C. or lower at atmospheric pressure.Preferred examples are formic acid, acetic acid, propionic acid, butyricacid, and isobutyric acid. With such compounds, it is easy to controlthe monocarboxylic acid content in the reaction system from mixingthrough heating, thus making it easy to strictly control the zinc oxidecrystal precipitation reaction. It is preferable to use the abovesaturated fatty acid in a proportion of 60 to 100 mol %, particularly 80to 100 mol %, in the total monocarboxylic acids. If the proportion islower than the above range, the zinc oxide particles in the compositeparticles tend to have reduced crystalline properties.

The monocarboxylic acid to be used further includes monocarboxylic acidzinc salts, e.g., zinc acetate. When such a zinc salt is used as a zincsource, it is not always necessary to separately add the above-mentionedmonocarboxylic acid.

The amount of the monocarboxylic acid to be used (or to be charged) forobtaining the first mixture is usually in a range of from 0.5 to 50 mol,preferably 2.2 to 10 mol, per mole of Zn atoms of the zinc source. Thisrange is advantageous for the economy, ease of composite particleformation, ease of obtaining composite particles which hardlyagglomerate and have excellent dispersibility. At a lower molar ratio toZn, zinc oxide fine particles having satisfactory crystalline propertiesand composite particles having uniformity in shape and size tend to behardly obtained. A higher molar ratio to Zn not only results in badeconomy but shows tendency to a failure of obtaining composite particleshaving satisfactory dispersibility.

The alcohols to be used can be those previously described with respectto the process for producing zinc oxide fine particles as described in(1) to (9) above. Those having a boiling point of 120° C. or higher atatmospheric pressure are preferred of them; for fine particles ofexcellent crystalline properties can be obtained with ease underatmospheric pressure and in a short time. For ease of obtainingparticles having excellent dispersibility, monohydric alcohols having aboiling point of 120° C. or higher and a water solubility of not lessthan 1% by weight at 20° C., for example, monoethers or monoesters ofglycols and n-butanol, are especially preferred.

While the amount of the alcohol is not limited, a preferred molar ratioof the alcohol to Zn atoms originated in the zinc source is 1 to 100,particularly 5 to 80, so that the formation of zinc oxide fine particlesmay be completed in a short time period. At a lower molar ratio, zincoxide fine particles with satisfactory crystalline properties are hardlyobtained, or composite particles excellent in dispersibility anduniformity in particle shape and size are hardly obtained. At a highermolar ratio, an economical disadvantage may result.

The alcohol may be used as a mixed solvent with water or organicsolvents other than alcohols, such as ketones, esters, aromatichydrocarbons, and ethers. The amount of the alcohol in thealcohol-containing solution used for preparation of the second mixtureis usually in a range of from 5 to 100% by weight, preferably 40 to 100%by weight, still preferably 60 to 100% by weight. If the proportion ofthe alcohol is lower than that range, composite particles satisfactoryin crystalline properties, uniformity in shape and size, anddispersibility tend to be hardly obtained.

The polymers which can be used in the process of the invention are thesame as those described with respect to the polymers constituting thecomposite particles of the invention.

While not limiting, the polymer is usually used in a weight ratio of0.01 to 1.0 to the zinc atoms, in terms of zinc oxide, contained in thezinc source (i.e., Zn atoms contained in the second mixture). At a lowerratio, composite particles tend to be hardly obtained. At a higherratio, precipitation of zinc oxide crystals tends to hardly occur,failing to obtain desired composite particles. While depending on thekind of the polymer or other reaction conditions, a preferred weightratio of the polymer to zinc, in terms of zinc oxide, is 0.05 to 0.8 forobtaining composite particles having a double layer structure, uniformparticle shape and size, and satisfactory dispersibility.

The process of the invention preferably comprises a first mixing stepand a second mixing step. The first mixing step is a step in which thezinc source and the carboxyl-containing compound are mixed to prepare afirst mixture containing zinc and the carboxyl-containing compound. Thesecond mixing step is a step in which the first mixture and the alcoholare mixed to prepare a second mixture having zinc and thecarboxyl-containing compound dissolved or dispersed in the medium.

According to the process of the invention, the polymer is added to anyone or more of the first mixing step, the second mixing step, and a stepof heating the second mixture to a temperature of 100° C. or higher. Thepolymer addition is conducted in any arbitrary stage before compositeparticles precipitate. For example, the polymer can be added to thefirst mixture during the first mixing step, to the second mixture duringthe second mixing step, or to the second mixture during the heatingstep.

The first mixing step is preferably a step in which the zinc source isdissolved in a mixed solvent of the carboxyl-containing compound andwater to provide a first mixture in a solution state.

The second mixing step is preferably a step in which the first mixtureis added to the alcohol maintained at 100° C. or higher to provide asecond mixture.

When the first mixture comprising the zinc source and thecarboxyl-containing compound is added to the alcohol, the first mixtureis preferably a solution. It is still preferable that the zinc sourceand the carboxyl-containing compound are mutually dissolved or they aredissolved in a solvent having high compatibility with both of them.Water, alcohols, ketones, and esters are advantageous as such a solventin that they easily dissolve the zinc source and the carboxyl-containingcompound at a temperature of from room temperature up to about 100° C.and that they are also highly compatible with the alcohol. The term“alcohols” as used above embraces all the alcohol species hereinabovedescribed.

Addition of the first mixture may be conducted at atmospheric pressure,under pressure, or under reduced pressure. Addition at atmosphericpressure is preferred from the economical viewpoint. In this case, whena dispersion of composite particles having uniformity in particle sizeand shape and excellent dispersibility is desired, it is preferable tokeep the alcohol at 60° C. or higher, particularly 100° C. or higher,especially 100° C. to 300° C., during addition and mixing. If thetemperature of the medium during addition and mixing is lower than 60°C., the viscosity of the second mixture tends to increase suddenlyduring or after addition and mixing, resulting in gelation. If thishappens, there arise such problems that stirring is impossible andunsuccessfully achieves uniform mixing or heat conduction in thesubsequent step, i.e., heating, is insufficient, resulting intemperature distribution. It follows that composite particles uniform incrystalline properties, particle size and particle shape can hardly beobtained. This problem also concerns the concentration of zinc in thesecond mixture and is more liable to occur at a higher zincconcentration. The lowest suitable temperature varies according to thepressure of the system. When the mixture is prepared under reducedpressure or under pressure, the temperature of the medium should beselected appropriately according to the pressure. When the first mixtureis added to the medium while keeping the medium at a temperature withinthe above range, part of the carboxyl-containing compound and/or part ofthe alcohol may be driven out of the system through evaporation.

Addition of the first mixture to the alcohol can be carried out byadding the whole amount of the first mixture to the alcohol all at once,or adding the first mixture dropwise to the alcohol, or spraying thefirst mixture onto the alcohol. In particular, continuous orintermittent dropwise addition of the first mixture on or into thealcohol is preferred for obtaining highly dispersible compositeparticles at high productivity.

The thus prepared first mixture is added to the alcohol kept at, e.g.,60° C. or higher, preferably 100° C. or higher, still preferably 100 to300° C., and mixed therewith to obtain the second mixture. In thepreparation of the second mixture by addition of the first mixture tothe medium, the first mixture is preferably added (by, for example,dropwise addition) while evaporating part of the volatile matter of thesecond mixture (e.g., the carboxyl-containing compound, the alcohol orwater).

For obtaining a uniform mixture, the alcohol is preferably stirred whilethe first mixture is being added thereto.

The polymer can be added in any of the above-described steps but beforeformation of composite particles.

For smooth spread of the polymer throughout the reaction system, it ispreferable for the polymer to be previously dissolved in the alcohol orbe added to the reaction system as dissolved in an arbitrary solvent.The solvent for dissolving the polymer is not particularly limited asfar as it is capable of dissolving the polymer, and can be selected fromorganic solvents, such as alcohols (the above-described ones), aliphaticor aromatic carboxylic acids, aliphatic or aromatic carboxylic acidesters, ketones, ethers, ether esters, aliphatic or aromatichydrocarbons, and halogenated hydrocarbons; water, mineral oil,vegetable oil, wax oil, silicone oil, and the like.

The second mixture is not limited provided that it is a mixture obtainedby mixing the above-described three essential components, i.e., a zincsource, a carboxyl-containing compound, and an alcohol, and the polymeris added thereto in any stage before formation of zinc oxide-polymercomposite particles. If desired, the mixture may contain componentsother than the three components, such as water; organic solvents, e.g.,ketones, esters, (cyclo)paraffins, ethers, and aromatic compounds;additives hereinafter described; metallic components other than zinc,e.g., inorganic metal salts (e.g., an acetate, a nitrate or a chloride)and organometallic alkoxides (e.g., metal alkoxides). The water ororganic solvents are usually used as a solvent component.

The state of the second mixture is not particularly limited and may be asolution, sol, an emulsion, a suspension, etc.

On heating the thus obtained second mixture at 100° C. or higher,preferably 100 to 300° C., still preferably 150 to 200° C., for a periodof 0.1 to 30 hours, preferably 0.5 to 10 hours, there are obtainedcomposite particles of the present invention with practical productivityin accordance with the kinds and ratio of the raw materials. That is, onmaintaining the second mixture at a temperature within the above rangefor a period within the above range, the zinc dissolved or dispersed inthe medium is converted to X-ray crystallographically crystalline zincoxide. Because the medium also has dissolved or dispersed therein thepolymer, the polymer forms a composite while the nuclei of zinc oxidecrystals precipitate and grow, thereby forming a dispersion containingzinc oxide-polymer composite particles. The internal structure, shapeand size of the composite particles formed, and the particle size of thezinc oxide fine particles present therein can be controlled by selectingthe kinds of the raw materials (e.g., the polymer and the alcohol) andby controlling the composition and temperature of the reaction system atthe time when composite particles are formed through control of thecomposition of raw materials charged and the thermal history appliedtill composite particles are formed.

The existing state of the individual components in the second mixture isnot particularly limited. In the reaction step wherein zinc dissolved ordispersed in the medium is converted to zinc oxide crystals, there arecases in which the reaction sometimes involves formation of one or morezinc oxide precursors. The case of using zinc oxide as a zinc source maybe mentioned as an example. The term “zinc oxide precursors” means ionsor compounds other than zinc oxide which contain at least a zinc atom.For example, the precursors include a zinc (hydrate) ion (Zn²⁺), apolynuclear zinc hydroxide ion, and (basic) carboxylic acid salts, suchas (basic) zinc acetate, (basic) zinc salicylate, and (basic) zinclactate. The precursor may be present with a part or the whole thereofforming a composite with the carboxyl-containing compound and/or thealcohol as, for example, a complex salt.

To set the heating temperature of the second mixture within the aboverange brings about the advantage that strict control on the compositionof the reaction system for obtaining zinc oxide fine particles,inclusive of control on the rate of evaporation of excessive orunnecessary components and the amount of evaporated components, can betaken easily. As a result, the particle size and the like of theresulting fine particles can be controlled easily. In the case when thefirst mixture is added to the above medium kept at 100° C. or higher toobtain the second mixture at 100° C. or higher, the resulting secondmixture is maintaining at that temperature, or the mixture is heated orcooled to a prescribed temperature, followed by heating. In the casewhen the first mixture is added to the above medium below 100° C., theresulting second mixture is heated to 100° C. or higher.

In the stage when zinc in the second mixture is converted to zinc oxidefine particles, the carboxyl-containing compound in the second mixturedoes not change or partly or totally undergoes esterification with apart or the whole of the alcohol in the second mixture to form an estercompound.

In the step for obtaining the dispersion, the alcohol, the aforesaidester compound produced on heating, or the solvent which may, ifdesired, have been added in the mixture may be removed by evaporationpartially.

Where the second mixture contains water, it is preferable to evaporatethe water to reduce the free water content of the resulting dispersionto 5% by weight or lower, particularly 1% by weight or lower. If thewater content exceeds the above level, cases are sometimes met with thatthe zinc oxide crystals in the composite fine particles have reducedcrystalline properties, resulting in a failure of fulfilling thefunction of zinc oxide, while such depends on the kinds of the othercomponents present in the dispersion, such as the alcohol.

It is preferable that the amount of the carboxyl-containing compound ina finally obtained composite particle dispersion be 0.5 mol or less permole of the total zinc atoms present in the dispersion. If it exceeds0.5 mol, cases are sometimes met with that the zinc oxide fine particleshave reduced crystalline properties, failing to fulfill the function ofzinc oxide. Accordingly, where the amount of the carboxyl-containingcompound present in the second mixture is such that the amount of thecarboxyl-containing compound in the finally obtained dispersion willexceed 0.5 mol per mole of the total zinc atoms in the resultingdispersion, at least the excess should be removed by evaporation duringthe heating step Needless to say, the carboxyl-containing compound maybe evaporated during heating even if the above molar ratio is 0.5 orlower.

Thus, the process of the invention provides a dispersion comprising 1 to80% by weight of zinc oxide-polymer composite particles which containzinc oxide fine particles and a polymer and have a number averageparticle size of 0.1 to 10 μm and a coefficient of particle sizevariation of not more than 30% (preferably a number average particlesize of 0.1 to 5 μm and a coefficient of size variation of not more than15%) in an alcohol and/or an ester compound and/or an organic solvent.

The dispersion of the composite particles obtained by the process of theinvention can be used as such. If desired, the dispersion can easily bepowdered or transformed to a dispersion of the composite particles in adifferent medium by solvent substitution.

Powder of zinc oxide can be obtained by separating the compositeparticles from the dispersion in a conventional manner, such asfiltration, centrifugation or solvent evaporation, followed by dryingor, if desired, calcination. A powdering method in which the dispersion(or a concentrated dispersion) is evaporated to remove the solvent bymeans of a vacuum flash evaporator is preferred for obtaining powderedcomposite particles having excellent dispersibility; for secondaryagglomeration of the composite particles, which often occurs duringdrying, can be suppressed in this method.

A dispersion of the composite particles in a solvent different from thatof the dispersion as produced by the process of the invention can beobtained by a known method comprising mixing the powder prepared by theabove-described powdering method with a desired solvent such as waterand dispersing the mixture with mechanical energy by means of a ballmill, a sand mill, an ultrasonic homogenizer, etc. A dispersion in adifferent solvent can also be prepared by mixing the dispersion asproduced with a desired solvent while heating the dispersion toevaporate part or the whole of the solvent to be replaced (solventsubstitution under heating). The solvent to be substituted for theinitial one is not particularly limited and includes organic solvents,such as alcohols, aliphatic or aromatic carboxylic acid esters, ketones,ethers, ether esters, aliphatic or aromatic hydrocarbons, andhalogenated hydrocarbons; water, mineral oil, vegetable oil, wax oil,silicone oil, and the like. A suitable solvent can be selectedappropriately according to the end use.

In what follows, the process for producing inorganic compound particleshaving, on their surface, a cluster of thin plate like zinc oxidecrystals with their tip projecting outward as described in (19) to (26)above and the inorganic compound particles as described in (43) to (49)above are explained.

The inorganic compound particles according to the invention contain 60to 100% by weight of zinc oxide and have on their surface a cluster ofthin plates whose tips projecting outward.

The process of the invention for producing the inorganic compoundparticles comprises maintaining a mixture of a zinc source and acarboxyl-containing compound dissolved or dispersed in a mediumcomprising at least an alcohol at a temperature of 100° C. or higher inthe presence of lactic acid or a compound thereof thereby to precipitateinorganic compound fine particles containing 60 to 100% by weight ofzinc oxide and having on the surface thereof a cluster of thin platelike zinc oxide crystals with their tips projecting outward.

The inorganic compound particles of the invention are not particularlylimited in shape and size.

The shape of the inorganic compound particles is not particularlylimited and can be, for example, a spherical or nearly spherical shape,a cylindrical shape, a column shape, a hexagonal prism shape, a spindleshape, a pyramidal shape or a cubic shape. Inorganic compound particleshaving at least one shape selected from a spherical shape and a nearlyspherical shape are easily dispersed and hardly broken by mechanicalshear when compounded into coating compositions or resins. The term“spherical” as used herein means that the particle assumes a round shapeas a whole with its L/B ratio (major axis (L)/minor axis (B)) being 1.0or greater and smaller than 1.2. The term “nearly spherical” as usedherein means that the particle assumes a round shape as a whole with itsL/B ratio being 1.2 to 5.0. Particles having an L/B ratio greater than5.0 tend to be hardly dispersed in resins or be easily broken bymechanical shear. The major axis (L) is the longest of measured threeaxes of the inorganic compound particle, and the minor axis (B) is thesmaller of the width and the height out of the three axes.

Of the inorganic compound particles of the invention, those having anumber average particle size of 0.1 to 10 μm, the particle size beingbased on the major axis (L), with a coefficient of size variation of notmore than 30%, particularly a number average particle size of 0.1 to 10μm with a coefficient or size variation of not more than 15% arepractically useful. If the number average particle size is smaller than0.1 μm, the above-described effects of design and beautiful appearancemay not be exerted. If it exceeds 10 μm, the particles, when formulatedinto coating compositions, tend to have poor dispersion stability. Ifthe coefficient of particle size distribution is more than 30%, there isa tendency that the particles have reduced dispersibility.

The inorganic compound particles of the invention may be hollow. Whenthe particles are hollow, the abnormal light scattering and transmittingcharacteristics become remarkable to provide an improved light filteringfunction. When the inorganic compound particles are hollow and/or haveinterstices among the thin plates, they exhibit improved adhesion to amatrix component or a matrix resin when formulated into a compositionand perform functions as porous particles or microcapsules. That is,they have functions of adsorption, separation, removal, and collection,such as oil absorptivity, hygroscopicity, harmful metal ionadsorptivity, harmful gas and bad order absorptivity; heat and soundinsulating functions (e.g., heat insulating fillers or sound insulatingfillers); a function of immobilizing metal ions, enzymes or bacteria(e.g., catalytic carriers and fillers for chromatography); light weightproperties; and a function of slowly releasing a liquid or perfume heldtherein.

The inorganic compound particles contain 60 to 100% by weight,preferably 80 to 100% by weight, of zinc oxide. If the proportion ofzinc oxide is lower than 60%, the mechanical strength of the particlesare reduced. The zinc oxide generally exhibits an X-ray diffractionpattern of any of a hexagonal system (wurtzite structure), a cubicsystem (rock salt structure), and a face-centered-cubic structure.Accordingly, as long as the amount of zinc atoms and oxygen atoms fallswithin the above range, the inorganic compound particles of theinvention include those in which a metal element other than zinc, e.g.,an alkali metal or an alkaline earth metal, forms, in the form of itsatom or ion, a composite with zinc oxide crystals; those in which aninorganic compound of a metal element other than zinc, e.g., an oxide, ahydroxide, a sulfide, a nitride, a carbide or a carbonate, forms a solidsolution in zinc oxide crystals; those in which an organometalliccompound, such as a silane, aluminum, zirconium or titanium couplingagent, an organosiloxane or a chelate compound, is bound to the surfaceof the zinc oxide crystals or forms a coating layer on the surface ofthe zinc oxide crystals; and those containing a halogen element, aninorganic acid radical (e.g., a sulfuric acid radical and a nitric acidradical) or an organic compound residue (e.g., a fatty acid residue, analcohol residue or an amine residue) in the inside and/or on the surfacethereof.

The inorganic compound particles of the invention have a cluster of thinplates with their tips facing outward. As far as the thin platesconstituting the cluster mainly comprise the inorganic compound asdescribed above and have their tips facing outward, the structure of thecluster is not particularly limited. For example, the other end of theindividual thin plates may be either separated from each other or beintimately close by cohesion, or the thin plates may be linked togetherat the portion mainly comprising the inorganic compound. It ispreferable, however, that the thin plates mainly comprising theinorganic compound are stacked and/or gathered radially. In this case,the above-mentioned abnormal light transmission characteristics becomeappreciable to bring about enhanced effects of design and improvedappearance.

The thin plates constituting the cluster are flat, having a flatness(major axis (l)/thickness (t)) of 2 to 200, preferably 4 to 100. If theflatness (l/t) is smaller than 2, the light filtering function, which isone of the characteristics based on the thin shape, tends to be reduced.If the flatness is greater than 200, the thin plates tend to havereduced mechanical strength. From the standpoint of industrial utilityof the particles, the thin plates constituting the cluster preferablyhave a major axis (l) ranging from 5 to 1000 nm, particularly from 50 to400 nm. If the major axis is shorter than 5 nm, the light filteringfunction, which is one of the characteristics based on the thin shape,tends to be reduced. If it exceeds 1000 nm, the thin plates tend to havereduced mechanical strength. The thin plates preferably have a thickness(t) ranging from 1 to 100 nm, particularly 2 to 50 nm. If the thicknessis smaller than the above range, the thin plates tend to be brokenmechanically. It if exceeds the above range, the visible lighttransmission tends to be reduced. The major axis (l) and the thickness(t) as referred to herein denote the length and the height of the threeaxes measured on the thin plate.

Since the inorganic compound particles of the invention contain 60 to100% by weight of zinc oxide and have on their surface a cluster of thinplates having their tips outward, they have the followingcharacteristics which were not possessed by conventional inorganiccompound particles or zinc oxide fine particles.

(a) They have abnormal light scattering and transmitting properties (atransmitted light filtering function). They are therefore useful as anartistic filler with beautiful color.

(b) They scatter electromagnetic waves in the near infrared regionwithout reducing the diffused transmission in the visible region.Therefore, they are useful as an infrared light-cutting filler havingtransparency.

(c) They are rich in surface unevenness.

It is desirable that all the inorganic compound particles of theinvention have the same shape and the above-mentioned coefficient ofparticle size variation. A film having such particles dispersed thereinhas fine surface unevenness owing to the individual fine particlesprojecting on the surface of the film. In addition, because theparticles are relatively regular in size and shape, the particles arewell dispersed in the film without aggregating. As a result, theprojections comprising the particles on the surface of the film arerelatively regular in size to give uniform surface unevenness and alsoprovide the surface with slip properties or anti-blocking propertieswithout impairing surface flatness. When the inorganic compound fineparticles of the invention are used like this, they exhibit excellentadhesion to a matrix resin (of a film) or a binder component (of acoating film) through the anchor effect of their surface unevenness.Thus, the particles can get rid of the problem of fall-off which hasbeen accompanied by conventional spherical particles having a smoothsurface.

The inorganic compound particles of the invention additionally have thefollowing characteristics (d) to (f) as well as the characteristics (a)to (c).

(d) They have high UV screening power.

(e) They are light semi-conductors.

(f) They have antimicrobial activity and antifungal activity.

When the inorganic compound particles are porous, especially when theyare porous and hollow, they have the following characteristics (g) and(h) in addition to (a) to (f).

(g) They have excellent adsorptivity for, for example, acidic or basiccompounds, such as fatty acids, amines and sulfur oxide, which causesmell and are therefore useful as a deodorant.

(h) They have controlled release properties. For example, the inorganiccompound particles having adsorbed an aromatic component can release thearomatic component at a controlled rate of release. The rate of slowrelease and the amount of adsorption can be controlled by adjusting thepore size or the porosity of the particles.

The particles of the invention are excellent in heat resistance and cannot only be compounded into those resins which are molded at hightemperatures, such as polyesters and polycarbonates, but can be appliedto the surface of glass, etc. with the aid of an inorganic binder toform a coating film, which can then be heated at a high temperature.Thus, the applicability of the particles is not restricted thermally.

The process for producing the inorganic compound particles of theinvention is not particularly limited.

The inorganic compound particles of the invention can be produced by theprocess of the present invention with good productivity.

According to the process of the invention, a mixture of zinc and acarboxyl-containing compound dissolved or dispersed in a mediumcomprising at least an alcohol is heated to a temperature of 100° C. orhigher in the presence of lactic acid or a compound thereof to therebyprecipitating inorganic compound particles containing 60 to 100% byweight of zinc oxide and having on their surface a cluster of thin platelike zinc oxide crystals having tips projecting outward.

Useful zinc sources and preferred examples thereof can be thosepreviously described with respect to the process for producing zincoxide fine particles as described in (1) to (9) above. Particularlypreferred among them are zinc oxide and/or zinc hydroxide because oftheir availability at low prices and freedom of choice of thecarboxyl-containing compound to be combined with. Starting with thesezinc sources, it is easy to obtain particles having a controlledparticle size and in which the thin crystals have controlled three axes.

The amount of the zinc source to be used is, for example, 0.1 to 95% byweight, preferably 0.5 to 50% by weight, still preferably 1 to 30% byweight, in terms of ZnO, based on the total amount of the zinc source,the carboxyl-containing compound, and the alcohol. If the zinc source isless than the above range, the productivity tends to decrease. If it ismore than the above range, fine particles having satisfactorydispersibility and a narrow particle size distribution tend to be hardlyobtained.

Useful carboxyl-containing compounds and preferred examples thereof canbe those previously described with respect to the process for producingzinc oxide fine particles as described in (1) to (9) above.Monocarboxylic acids are particularly preferred.

Useful monocarboxylic acids and preferred examples thereof can be thosepreviously described with respect to the process for producing thecomposite particles as described in (10) to (18) above.

Preferred of the monocarboxylic acids are saturated fatty acids having aboiling point of 200° C. or lower at atmospheric pressure. Preferredexamples are formic acid, acetic acid, propionic acid, butyric acid, andisobutyric acid. With such compounds, it is easy to control themonocarboxylic acid content in the reaction system from mixing throughheating, thus making it easy to strictly control the precipitationreaction of zinc oxide crystals. It is preferable to use the saturatedfatty acid in a proportion of 60 to 100 mol %, particularly 80 to 100mol %, in the total monocarboxylic acids. If the proportion is lowerthan 60 mol %, the crystalline properties of zinc oxide in the fineparticles tends to be reduced.

The monocarboxylic acid to be used further includes monocarboxylic acidzinc salts, e.g., zinc acetate. When such a zinc salt is used as a zincsource, it is not always necessary to separately add the above-mentionedmonocarboxylic acid.

The amount of the monocarboxylic acid to be used (or to be charged) forobtaining the mixture is in a range of, for example, from 0.5 to 50 mol,preferably 2.2 to 10 mol, per mole of Zn atoms of the zinc source used.This range is advantageous for the economy, ease of formation of fineparticles, and ease of obtaining fine particles having excellentdispersibility. At a lower molar ratio to Zn, zinc oxide fine particleswith satisfactory crystalline properties and fine particles havinguniformity in shape and size tend to be hardly obtained. A higher molarratio to Zn not only results in bad economy but shows tendency to afailure of obtaining fine particles having satisfactory dispersibility.

The alcohols to be used can be those previously described with respectto the process for producing zinc oxide fine particles as described in(1) to (9) above. Those having a boiling point of 120° C. or higher atatmospheric pressure are preferred of them; for fine particles ofexcellent crystalline properties can be obtained with ease underatmospheric pressure and in a short time. For ease of obtainingparticles having excellent dispersibility, monohydric alcohols having aboiling point of 120° C. or higher and a water solubility of not lessthan 1% by weight at 20° C., for example, monoethers or monoesters ofglycols and n-butanol, are especially preferred.

While the amount of the alcohol is not particularly limited, a preferredmolar ratio of the alcohol to Zn atoms originated in the zinc source is1 to 100, particularly 5 to 80, especially 10 to 50, so that theformation of zinc oxide fine particles may be completed in a short timeperiod. At a lower molar ratio, zinc oxide fine particles withsatisfactory crystalline properties are hardly obtained, or particlesexcellent in dispersibility and uniformity in particle shape and sizeare hardly obtained. At a higher molar ratio, an economical disadvantagemay result.

The alcohol may be used as a mixed solvent with water or organicsolvents other than alcohols, such as ketones, esters, aromatichydrocarbons, and ethers. The proportion of the alcohol in the mixedsolvent is usually in a range of from 5 to 100% by weight, preferably 40to 100% by weight, still preferably 60 to 100% by weight, in terms ofproportion in the total mixed solvent charged (or used) for preparationof the mixture. If the proportion of the alcohol is lower than thatrange, particles satisfactory in crystalline properties, uniformity inshape and size, and dispersibility tend to be hardly obtained.

Lactic acid or a compound thereof which can be used in the inventionincludes lactic acid; lactic acid metal salts, such as ammonium lactate,sodium lactate, lithium lactate, calcium lactate, magnesium lactate,zinc lactate, aluminum lactate, manganese lactate, iron lactate, nickellactate, and silver lactate; and lactic ester compounds capable ofgenerating lactic acid on hydrolysis, etc., such as methyl lactate,ethyl lactate, and n-butyl lactate. These compounds may be used eitherindividually or as a combination of two or more thereof.

While not limiting, lactic acid or a compound thereof is preferably usedat a molar ratio of 0.001 to 0.4 to zinc in the mixture. If the lacticacid to Zn molar ratio is lower than 0.001, the effect of the presenceof lactic acid tends to be insufficient for obtaining thin plate likezinc oxide crystals. At a higher molar ratio, precipitation reaction ofzinc oxide crystals tends to hardly take place, failing to obtaindesired particles. In order to obtain particles regular in shape, themolar ratio of lactic acid (or a compound thereof) to zinc is preferablyin the range of from 0.001 to 0.2. In order to obtain particles regularin size and having satisfactory dispersibility, the molar ratio oflactic acid (or a compound thereof) to zinc is preferably in the rangeof from 0.001 to 0.1.

It is preferable that the process of the invention preferably comprisesa first mixing step of preparing a first mixture comprising a zincsource and a carboxyl-containing compound and a second mixing step inwhich the first mixture is added and mixed with a heatedalcohol-containing solution, and that lactic acid or a compound thereofbe added in at least one step selected from the first mixing step andthe second mixing step.

It is particularly preferable that the process of the inventioncomprises the following steps (I) through (III), and lactic acid or acompound thereof is added in at least one step selected from the groupconsisting of steps (I), (II), and (III).

(I) A step of preparing a first mixture comprising a zinc source and acarboxyl-containing compound.

(II) A step of mixing the first mixture with an alcohol to prepare asecond mixture comprising the alcohol having dissolved or dispersedtherein zinc and the carboxyl-containing compound.

(III) A step of maintaining the second mixture at a temperature of 100°C. or higher thereby to precipitate inorganic compound particlescontaining 60 to 100% by weight of zinc oxide and having on theirsurface a cluster of thin plate like zinc oxide crystals with their tipsprojecting outward.

Step (I) is preferably a step of dissolving the zinc source in a mixedsolvent of the carboxyl-containing compound and water to obtain thefirst mixture in a solution state.

Step (II) is preferably a step of adding the first mixture to a mediumcomprising at least the alcohol and kept at a temperature of 100° C. orhigher to obtain the second mixture.

When the first mixture comprising the zinc source and thecarboxyl-containing compound is added to the alcohol, it is preferablethat the first mixture be a solution. In this case, it is desirable forthe zinc source and the carboxyl-containing compound to be dissolvedmutually or to be dissolved in a solvent having high compatibility toboth of them. Water, alcohols, ketones, and esters are advantageous assuch a solvent in that they easily dissolve the zinc source and thecarboxyl-containing compound at a temperature of from room temperatureup to about 100° C. and that they are also highly compatible with theabove-mentioned solvent. The term “alcohols” as used above embraces allthe alcohol species hereinabove described.

Addition of the first mixture may be conducted at atmospheric pressure,under pressure, or under reduced pressure. Addition at atmosphericpressure is preferred from the economical viewpoint. In this case, whena dispersion of fine particles having uniformity in particle size andshape and excellent dispersibility is desired, it is preferable to keepthe alcohol at 60° C. or higher, particularly 100° C. to 300° C., duringaddition and mixing. If the temperature of the alcohol during additionand mixing is lower than 60° C., cases are sometimes met with, in whichthe viscosity of the second mixture increases suddenly during or afteraddition and mixing, resulting in gelation. If this happens, there arisesuch problems that stirring is impossible and unsuccessfully achievesuniform mixing or heat conduction in the subsequent step, i.e., heating,is insufficient, resulting in temperature distribution. It follows thatfine particles uniform in crystalline properties, particle size andparticle shape can hardly be obtained. This problem also concerns theconcentration of zinc in the second mixture and is more liable to occurat a higher zinc concentration. The lowest suitable temperature variesaccording to the pressure of the system. When the mixture is preparedunder reduced pressure or under pressure, the temperature of the alcoholshould be selected appropriately according to the pressure. When thefirst mixture is added to the alcohol while keeping the alcohol at atemperature within the above range, part of the carboxyl-containingcompound and/or part of the alcohol may be driven out of the systemthrough evaporation.

Addition of the first mixture to the alcohol can be carried out byadding the whole amount of the first mixture to the alcohol all at once,or adding the first mixture dropwise to the alcohol, or spraying thefirst mixture onto the alcohol. In particular, continuous orintermittent dropwise addition of the first mixture on or into thealcohol is preferred for obtaining highly dispersible compositeparticles with high productivity.

The thus prepared first mixture is added to the alcohol kept at, e.g.,60° C. or higher, preferably 100 to 300° C., and mixed therewith toobtain the second mixture. In the preparation of the second mixture byaddition of the first mixture to the alcohol, the first mixture ispreferably added (by, for example, dropwise addition) while evaporatingpart of the volatile matter of the first mixture and/or the secondmixture (e.g., the carboxyl-containing compound, the alcohol or water).

For obtaining a uniform mixture, the alcohol is preferably stirred whilethe first mixture is being added thereto.

Lactic acid or a compound thereof can be added in any of theabove-described steps but before formation of particles containing acluster of thin plate like zinc oxide crystals. In using a metal lactateas lactic acid or a compound thereof, it is preferably added to thefirst mixture and dissolved therein in step (I), either together with azinc source separately added or as a zinc source (in the case of usingzinc lactate). This manner of addition is advantageous for obtainingparticles uniform in shape and size.

Addition of lactic acid or a compound thereof can be carried acid, forexample, as follows. In using lactic acid (CH₃CH(OH)COOH) and/or alactic ester, it can be added at any stage from step (I) through step(III) either directly or as dissolved in a solvent (e.g., an alcohol).The latter manner of addition is preferred for smooth spread of thelactic acid particularly when lactic acid or a compound thereof is addedin step (III). In using a metal lactate, it can be added at any stagefrom step (I) through step (III), and preferably it is dissolved in thefirst mixture together with the zinc source or as a zinc source. Forexample, a zinc source powder and a metal lactate powder are added to asolution containing the carboxyl-containing compound, followed bystirring to form a uniform solution. In this preparation, stirring whileheating is preferred for increasing the rate of dissolution andsolubility of each powder thereby to provide a high concentrationsolution in a short time.

The second mixture is not limited provided that it is a mixture obtainedby mixing the above-described three essential components, i.e., the zincsource, the carboxyl-containing compound, and the alcohol, and lacticacid or a compound thereof is added thereto at a stage before formationof particles containing a cluster of thin plate like zinc oxidecrystals. If desired, the mixture may contain components other than thethree components, such as water; organic solvents, e.g., ketones,esters, (cyclo)paraffins, ethers, and aromatic compounds; additiveshereinafter described; metallic components other than zinc components,e.g., inorganic metal salts (e.g., an acetate, a nitrate or a chloride)and organometallic alkoxides (e.g., metal alkoxides). Of thesecomponents, water and organic solvents are usually used as a solventcomponent.

The state of the second mixture is not particularly limited and may be asolution, sol, an emulsion, a suspension, etc.

On maintaining the thus obtained second mixture at 100° C. or higher,preferably 100 to 300° C., still preferably 150 to 200° C., for a periodof 0.1 to 30 hours, preferably 0.5 to 10 hours, still preferably 0.5 to5 hours, there is obtained inorganic compound particles of the presentinvention with practical productivity in accordance with the kinds andratios of the raw materials. That is, on maintaining the second mixtureat a temperature within the above range for a period within the aboverange, the zinc dissolved or dispersed in the medium is converted toX-ray crystallographically crystalline zinc oxide. Because the mediumalso has dissolved or dispersed therein lactic acid, the zinc oxidecrystals grow anisotropically to form thin plate like zinc oxidecrystals, thereby to obtain a dispersion containing inorganic compoundparticles whose surface is composed of the thin plate like zinc oxidecrystals that gather into a cluster with their tips facing outward. Withthe lactic acid to zinc molar ratio falling within the range of from0.001 to 0.4, the thin plate like zinc oxide crystals form a cluster ofthin plates having a flatness of 2 to 200 and a major axis of 5 to 1000nm.

The existing state of the individual components in the second mixture isnot particularly limited. In the reaction step wherein zinc dissolved ordispersed in the alcohol is converted to thin plate like zinc oxidecrystals, there are sometimes cases in which the reaction involvesformation of one or more zinc oxide precursors. The case of using zincoxide as a zinc source may be mentioned as an example. The term “zincoxide precursors” means ions or compounds other than zinc oxide whichcontain at least a zinc atom. For example, the precursors include a zinc(hydrate) ion (Zn²⁺), a polynuclear zinc hydroxide ion, and (basic)carboxylic acid salts, such as (basic) zinc acetate, (basic) zincsalicylate, and (basic) zinc lactate. The precursor may be present witha part or the whole thereof forming a composite with thecarboxyl-containing compound and/or the alcohol as, for example, acomplex salt.

To set the heating temperature of the second mixture within theabove-described range brings about the advantage that strict control onthe composition of the reaction system for obtaining zinc oxide fineparticles, inclusive of control on the rate of evaporation of excessiveor unnecessary components and the amount of evaporated components, canbe taken easily. As a result, the particle size and the like of theresulting fine particles can be controlled easily. In the case when thefirst mixture is added to the alcohol kept at 100° C. or higher toobtain the second mixture of 100° C. or higher, heating of the resultingsecond mixture can be achieved by maintaining the mixture at thattemperature, or the mixture is heated or cooled to a prescribedtemperature, followed by heating. In the case when the first mixture isadded to the alcohol below 100° C., the resulting second mixture isheated to 100° C. or higher.

In the stage of conversion of zinc in the second mixture into fineparticles, the carboxyl-containing compound in the second mixture doesnot change or partly or totally undergoes esterification with a part orthe whole of the alcohol in the second mixture to form an estercompound.

In the step for obtaining the dispersion, the alcohol, the aforesaidester compound produced on heating, or the solvent which may, ifdesired, have been added in the mixture may be removed by evaporationpartially or totally.

Where the second mixture contains water, it is preferable to evaporatethe water to reduce the free water content of the resulting dispersionto 5% by weight or lower, particularly 1% by weight or lower. If thewater content exceeds the above level, cases are sometimes met with inwhich the zinc oxide crystals in the fine particles have reducedcrystalline properties, resulting in a failure of fulfilling thefunction as zinc oxide, while such depends on the kinds of the othercomponents present in the dispersion, such as the alcohol.

It is preferable that the amount of the carboxyl-containing compound ina finally obtained dispersion be 0.5 mol or less per mole of the totalzinc atoms present in the dispersion. If it exceeds 0.5 mol, cases aresometimes met with that the zinc oxide fine particles have reducedcrystalline properties, failing to fulfill the function as zinc oxide.Accordingly, where the amount of the carboxyl-containing compoundpresent in the second mixture is such that the amount of thecarboxyl-containing compound in the finally obtained dispersion willexceed 0.5 mol per mole of the total zinc atoms in the resultingdispersion, at least the excess should be removed by evaporation duringthe heating step. Needless to say, the carboxyl-containing compound maybe evaporated during heating even if the above molar ratio is 0.5 orlower.

For the purpose of controlling the particle size, shape, and surfacepolarity of finally obtained particles, it is possible to conduct theheating step in the presence of a long-chain saturated fatty acid, suchas those having 6 to 20 carbon atoms (e.g., caprylic acid, lauric acid,myristic acid, palmitic acid, and stearic acid) (of thecarboxyl-containing compounds) and/or a specific additive. The time ofaddition of the additive is not particularly limited and is selectedappropriately according to the purpose and the kind of the additive.That is, the additive may be added in the step of preparing the secondmixture or the first mixture or the step of heat treatment. When asurface treatment is aimed, the additive is preferably added after theformation of the particles.

Examples of the above-mentioned specific additive include (1) aliphaticamines, such as octadecylamine and stearylamine, (2) various couplingagents including silane coupling agents, such as methyltrimethoxysilane,phenyltrimethoxysilane, benzyltriethoxysilane,γ-aminopropyltriethoxysilane,N-β(aminoethyl)γ-aminopropyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, andstearyltrimethoxysilane; titanate coupling agents, such asisopropyltriisostearoyl titanate, bis(dioctyl pyrophosphate)oxyacetatetitanate, tetraoactylbis(ditridecyl phosphite) titanate, andisopropyltri(N-aminoethylaminoethyl) titanate; and aluminum couplingagents, such as ethylacetacetatealuminum diisopropylate; and partialhydrolysis products thereof, (3) organophosphorus compounds includingphosphoric esters, such as trimethyl phosphate, triethyl phosphate,tributyl phosphate, tris(2-chloroethyl) phosphate, and(polyoxyethylene)bis[bis(2-chloroethyl)phosphate]; acid phosphoricesters, such as methyl acid phosphate, propyl acid phosphate, laurylacid phosphate, stearyl acid phosphate, bis-2-ethylhexyl phosphate, anddiisodecyl phosphate; phosphorous esters, such as trimethyl phosphite;and thiophosphoric esters, such as dimethyldithiophosphate anddiisopropyl dithiophosphate, (4) organopolysiloxanes containing in themolecule thereof at least one of the above-mentioned atomic groups, suchas an amino group (e.g., a primary amino group, a secondary amino group,a tertiary amino group, a quaternary ammonio group, etc.), a carboxylgroup, a sulfonic acid group, a phosphoric acid group, a hydroxyl group,and an epoxy group, (5) anionic surface active agents, such as sodiumlauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylenelauryl ether sulfate, a sodium dialkylsulfosuccinate, and calciumstearate, (6) nonionic surface active agents, such as polyoxyethylenelauryl ether, a polyoxyethylene alkylamine, polyethylene glycolmonolaurate, and glycerol monostearate, (7) cationic surface activeagents, such as lauryldimethylamine and stearyltrimethylammoniumchloride, (8) amphoteric surface active agents, such as lauryl betaineand stearylamine acetate, and (9) metallic soaps, such as calciumstearate. These additives may be used either individually or as acombination of two or more thereof.

According to the process of the invention, there is obtained adispersion containing 1 to 80% by weight of fine particles in a solventcomprising an alcohol and/or the above-described ester compound and/oran organic solvent, the fine particles having a number average particlesize of 0.1 to 10 μm with a coefficient of size variation of not morethan 30% and a uniform shape and the individual fine particlescomprising a stacked and/or radially gathered thin plate like zinc oxidecrystals with their tips facing outward.

The particle dispersion as produced by the process of the invention canbe used as such. If desired, the dispersion can easily be powdered ortransformed to a dispersion of the particles in a different medium bysolvent substitution.

Powder of the particles can be obtained by separating the particles fromthe dispersion medium in a conventional manner, such as filtration,centrifugation or solvent evaporation, followed by drying or, ifdesired, calcination. A powdering method in which the dispersion (or aconcentrated dispersion) is evaporated to remove the solvent by means ofa vacuum flash evaporator suppresses secondary agglomeration of fineparticles, which often occurs during drying, and is therefore preferredfor obtaining zinc oxide powder having excellent dispersibility.

If necessary, the resulting powder can be calcined. Calcination isusually carried out at 100° C. to 800° C. The calcining temperatureshould be decided appropriately so that the geometrical structure of theparticles and various physical and chemical properties attributed to thestructure may not be impaired. The calcining atmosphere is arbitrarilyselected according to the purpose. For example, calcination can beperformed in air or an inert gas atmosphere, such as nitrogen, helium orargon.

A dispersion of the particles in a solvent different from that of thedispersion as produced by the process of the invention can be obtainedby a known method comprising mixing the powder prepared by theabove-described powdering method with a desired solvent such as waterand dispersing the mixture with mechanical energy by means of a ballmill, a sand mill, an ultrasonic homogenizer, etc. A dispersion in adifferent solvent can also be prepared by mixing the dispersion asproduced with a desired solvent while heating the dispersion toevaporate part or the whole of the solvent to be replaced (solventsubstitution under heating). The solvent to be substituted for theinitial one is not particularly limited and includes organic solvents,such as alcohols, aliphatic or aromatic carboxylic acid esters, ketones,ethers, ether esters, aliphatic or aromatic hydrocarbons, andhalogenated hydrocarbons; water, mineral oil, vegetable oil, wax oil,silicone oil, and the like. A suitable solvent can be selectedappropriately according to the end use.

The process for producing zinc oxide-based particles described in (27)to (36) above and zinc oxide-based particles described in (50) to (58)will now be explained.

The zinc oxide-based particles according to the invention mainlycomprise a metal oxide co-precipitate which contains, as a metalliccomponent, zinc and at least one element additive selected from thegroup consisting of the group IIIB metal element and the group IVB metalelement, has a zinc content being 80 to 99.9% in terms of the ratio ofthe number of zinc atoms to the total number of the atoms of themetallic components, and exhibits zinc oxide (ZnO) crystallineproperties when X-ray crystallographically observed. The crystal form ofzinc oxide is not particularly limited and may have an X-ray diffractionpattern of any known structures, such as a hexagonal system (wurtzitestructure), a cubic system (rock salt structure), and aface-centered-cubic structure. The zinc content of the metal oxideco-precipitate ranges form 80 to 99.9%, preferably 90 to 99.5%, in termsof the ratio of the number of zinc atoms to the total number of theatoms of the metallic components. If the zinc atomic ratio is lower thanthe above range, the particles hardly have controlled uniformity inshape, size, higher-order structure, and the like. If the ratio ishigher than the above range, the functions as a co-precipitate, that is,infrared screening properties (inclusive of heat ray screeningproperties) become insufficient.

Therefore, as far as the above-described conditions are fulfilled, alsoincluded in the zinc oxide-based particles as referred to in theinvention are those in which an organometallic compound, such as acoupling agent (e.g., a silane coupling agent and an aluminum couplingagent), an organosiloxane or a chelate compound, is bound to the surfaceof the zinc oxide crystals or forms a coating layer on the surface ofthe zinc oxide crystals and those containing a halogen element, aninorganic acid radical (e.g., a sulfuric acid radical and a nitric acidradical) or an organic compound residue (e.g., a fatty acid residue, analcohol residue or an amine residue) in the inside and/or on the surfacethereof. It is not favorable that an alkali metal or an alkaline earthmetal (as a metallic element other than the element additive selectedfrom the group consisting of the group IIIB metal elements and the groupIVB metal elements and zinc) is present in the form of a solid solutionin ZnO crystals. The amount of these other metallic elements present inthe particles is preferably not more than {fraction (1/10)},particularly not more than {fraction (1/100)}, of the total number ofatoms of the element additive selected from the group consisting of thegroup IIIB metal elements and the group IVB metal elements. This doesnot apply where the particles are surface-treated with an alkalimetal-containing surface active agent, etc.

The element additive which constitutes the metal oxide co-precipitate isat least one member selected from the group consisting of the group IIIBmetallic elements, e.g., boron, aluminum (Al), gallium (Ga), indium(In), and thallium (Tl), and the group IVB metallic elements, e.g.,silicon (Si), germanium (Ge), tin (Sn), and lead (Pb). Of these metallicelements, indium and/or aluminum is/are particularly preferred.

The zinc oxide-based particles of the invention embrace threeembodiments; in the first embodiment the individual particle exists inthe form of a single particle comprising the metal oxide co-precipitate;in the second embodiment a plurality of the single particles gather toform the individual particle; and in the third embodiment the singleparticles form a composite with a polymer. These three embodiments willfurther be explained below.

In the first embodiment, each zinc oxide-based particle is made upsolely of a single particle of the metal oxide co-precipitate. Thesingle particle preferably has an average particle size of 0.001 to 0.1μm, particularly 0.001 to 0.05 μm, in its shortest dimension.

Unless otherwise specified, the term “particle size”, inclusive ofaverage particle size, a number average particle size, and the like asused with respect to the zinc oxide-based particles is intended todenote the diameter in the shortest dimension. The term “diameter in theshortest dimension” as used above means the shortest of the diameterspassing the center of the particle. In other words, the “particle size”means the diameter of a spherical fine particle; the minor axis of anellipsoidal fine particle; the shortest of the axes passing the centerof a cubic particle, a rectangular parallelepiped particle or apyramidal particle; the length of the axis which passes the center andis perpendicular to the longitudinal axis of an acicular, column, rod orcylindrical particle; or the shortest axis passing the center in thedirection perpendicular to the main surface, i.e., the thicknessdirection, (=thickness) of a flaky or (hexagonal) tabular particle.

The longest diameter of granular or spherical particles preferably fallswithin the same range as the shortest diameter, and that of odd-shapedparticles (e.g., thin plates and needles or acicular particles) ispreferably 0.002 μm or longer and smaller than 0.5 μm. The shape of themetal oxide co-precipitate or zinc oxide-based particles is arbitraryand may be, for example, a thin plate, e.g., a flaky shape or a(hexagonal) tabular shape; an acicular shape, a column shape, a rodshape, a cylindrical shape; a granular shape, e.g., a cubic shape or apyramidal shape; and a spherical shape.

In the second embodiment, the zinc oxide-based particles are secondaryparticles made by gathering of the above-mentioned single particles as aprimary particle. In this embodiment, the secondary particles mayconstitute only an outer shell to provide hollow particles. When theparticles are hollow and also when the primary particles have a size offrom 0.005 to 0.1 μm, particularly 0.005 to 0.05 μm, excellent diffusedtransmission properties are exerted. In this case, the ratio of theshortest particle size of the single particle to the shortest particlesize of the zinc oxide-based particles (i.e., an agglomerate of thesingle particles) is preferably not more than {fraction (1/10)}.

In the third embodiment, the zinc oxide-based particles are compositeparticles comprising the above-mentioned single particles and a polymer.The structure of the composite is arbitrary. For example, (A) a polymercovers the surface of a single particle and/or the surface of anagglomerate of a plurality of the single particles, (B) a polymer bindsthe single particles together, and (C) a polymer constitutes a matrix inwhich the single particles are dispersed without being agglomeratedand/or agglomerates of a plurality of the single particles aredispersed. The composite particles having structure (B) or (C) may alsobe hollow particles, the outer shell of which is composed of the singleparticles and the polymer. When the composite particles are hollow andhave a primary particle size of 0.005 to 0.1 μm, particularly 0.005 to0.05 μm, they have excellent diffused transmission properties in thesame manner as in the second embodiment. In this embodiment, the amountof the polymer, while not limiting, usually ranges from 1 to 90% byweight based on the total amount of the single particle(s) and thepolymer.

The polymer to be used in the composite particles of the thirdembodiment can be those described with reference to the zincoxide-polymer composite particles described in (10) to (19) above.

In the second embodiment and the structures (B) and (C) of the thirdembodiment, the zinc oxide-based particles preferably have a sphericalor ellipsoidal shape. It is preferable for the surface of theseparticles to have fine surface unevenness irrespective of the contour ofthe particles because the surface unevenness synergistically contributesto light scatter on the surface to provide improved light scatteringpower. In the second and third embodiments, the average particle size ofthe zinc oxide-based particles is not particularly limited but usuallyranges from 0.001 to 10 μm. In the structure (A) of the thirdembodiment, an average particle size of 0.001 to 0.1 μm is preferred forhigh transparency. Hollow particles preferably have an average particlesize of 0.1 to 5 μm for high diffuse transmission power.

The zinc oxide-based particles of the invention are sometimes used as adispersion in a solvent. Useful media include water, alcohols, ketones,aliphatic or aromatic carboxylic acid esters, ethers, ether esters,aliphatic or aromatic hydrocarbons, halogenated hydrocarbons, mineraloil, vegetable oil, wax oil, silicone oil, and the like. In addition tothese solvents, the dispersion may contain other components, forexample, organic binders or inorganic binders used as a binder forcoating compositions. Useful organic binders include thermoplastic orthermosetting resins, such as (meth)acrylic resins, vinyl chlorideresins, silicone resins, melamine resins, urethane resins, styreneresins, alkyd resins, phenolic resins, epoxy reins, and polyesterresins; and synthetic rubbers, such as ethylene-propylene copolymerrubber, polybutadiene rubber, and acrylonitrile-butadiene rubber ornatural rubber. Useful inorganic binders include silica sol, alkalisilicates, silicon alkoxides, and phosphates.

The process for producing the zinc oxide-based particles is explainedbelow.

The process for producing the zinc oxide-based particles according tothe present invention comprises heating a zinc source and acarboxyl-containing compound to a temperature of 100° C. or higher in analcohol in the presence of a compound containing at least one elementadditive selected from the group consisting of the group IIIB metallicelements and the group IVB metallic elements to thereby form particles.The group IIB metallic elements can be those described above, withindium and/or aluminum being preferred as described above.

The process of the invention preferably comprises a first mixing step ofpreparing a first mixture comprising a zinc source and acarboxyl-containing compound and a second mixing step of mixing thefirst mixture with a heated alcohol-containing solution, and the elementadditive is preferably added in at least one step selected from thefirst mixing step and the second mixing step.

Still preferably, the process comprises a first mixing step of preparinga first mixture comprising a zinc source and a monocarboxylic acid, asecond mixing step of mixing the first mixture with an alcohol toprepare a second mixture, and a heating step of heating the secondmixture at a temperature of 100° C. or higher, and a compound containingat least one element additive selected from the group consisting of thegroup IIIB metallic elements and the group IVB metallic elements isadded to the first mixture and/or the second mixture in any of thesesteps. The compound containing the element additive may be added eitheralone or as dissolved in an alcohol. The first mixing step is preferablycarried out by dissolving the zinc source in a mixed solvent of thecarboxyl-containing compound and water.

The process preferably includes a step in which a mixture of the zincsource and the carboxyl-containing compound in water is added to thealcohol heated to 100° C. or higher thereby to remove at least part ofthe water and/or the carboxyl-containing compound by evaporation. Whilethe zinc source and the carboxyl-containing compound are preferably usedas dissolved in water, it is desirable to drive water or thecarboxyl-containing compound out of the system as much as possible so asto prevent reduction of the crystalline properties of the fine particlesand also to prevent secondary agglomeration thereby to secure uniformityin size and shape of the fine particles. Formation of fine particles mayoccur during addition of the first mixture to the heated medium but isusually induced by maintaining the reaction system after the addition ata temperature of 100° C. or higher. Meanwhile, evaporation of water andthe carboxyl-containing compound is usually observed.

The zinc source to be used in the process of the invention is, forexample, at least one member selected from the group consisting of zincoxide, zinc hydroxide, and zinc acetate. The carboxyl-containingcompound is preferably a saturated fatty acid having a boiling point of200° C. or lower at atmospheric pressure.

When the zinc source and the carboxyl-containing compound are maintainedat a temperature of 100° C. or higher in an alcohol in the presence of acompound containing at least one element additive selected from thegroup consisting of the group IIIB metallic elements and the group IVBmetallic elements, the system may contain (1) a polymer, (2) a compoundadditive containing, in the molecule thereof, one or more than oneatomic groups selected from the group consisting of a carboxyl group, anamino group, a quaternary ammonio group, an amido group, an imido bond,an alcoholic and/or phenolic hydroxyl group, a carboxylic acid esterbond, a urethane group, a urethane bond, a ureido group, a ureylenebond, an isocyanate group, an epoxy group, a phosphoric acid group, ametallic hydroxyl group, a metallic alkoxy group, and a sulfonic acidgroup and having a molecular weight of smaller than 1000, (3) carbondioxide and/or a carbonic acid source, or (4) lactic acid or a compoundthereof.

Where a polymer is present in the system maintained at 100° C. orhigher, zinc oxide-based composite particles comprising theabove-described single particles and a polymer are obtained. Suitablepolymers to be used can be those described with respect to the compositeparticles according to (10) to (18) above.

Where a compound having the above-described specific functional group ispresent in the system maintained at 100° C. or higher, it is possible toconduct surface treatment of the particles, and the particle size iscontrollable.

Where carbon dioxide and/or a carbonic acid source is present in thesystem maintained at 100° C. or higher, fine particles having excellentwater dispersibility and high fineness (0.05 μm or smaller) can beobtained with ease. (Basic) zinc carbonate when used as part of a zincsource will serve in substitution for a carbonic acid source. A suitableamount of a carbonic acid source is 0.1 to 20 mol % based on zinc. Toomuch carbonic acid sometimes interferes with crystallization of zincoxide, and such being the case, the heating temperature must beincreased. Carbonic acid sources include compounds producing carbonateions or carbon acid gas on, e.g., heating, such as ammonium carbonate,ammonium hydrogencarbonate, and urea; metal carbonates, such as yttriumcarbonate, cadmium carbonate, silver carbonate, samarium carbonate,zirconium carbonate, cerium carbonate, thallium carbonate, leadcarbonate, and bismuth carbonate; and basic metal carbonates, such asbasic zinc carbonate, basic cobalt(II) carbonate, basic copper(II)carbonate, basic lead(II) carbonate, and basic nickel(II) carbonate.These carbonic acid sources can be used either individually or as acombination of two or more thereof.

The process of maintaining the system at 100° C. or higher in thepresence of lactic acid or a compound thereof is effective in obtainingsecondary particles that are agglomerates of the single particlescomprising the metal oxide co-precipitate as a primary particle.

Lactic acid or a compound thereof to be used can be those described withrespect to the process for producing inorganic compound particlesdescribed in (43) to (49) above.

The zinc oxide-based particles according to the invention will furtherbe illustrated in detail. here the zinc oxide-based particles of theinvention are single particles of the metal oxide co-precipitate(embodiment (1)), the single particles may be dispersed uniformly or maybe partly agglomerated. In this case, where the single particles have anaverage particle size of 0.001 to 0.05 μm, particularly 0.02 μm orsmaller, they are useful as a material of transparent films that screenultraviolet rays or heat rays. Where the single particles as primaryparticles are agglomerated to form an outer shell composed of thesecondary particles (embodiment (2)), the secondary particles have adouble layer structure. In this case, the particles exhibit high lightdiffusing properties as well as high light transmitting propertiesbecause, in addition to light scatter on the surface of the secondaryparticles (corresponding to light scatter on conventional inorganictransparent fine particles), light is also scattered on the surface ofthe primary particles in the secondary particles and on the interfacebetween the outer shell and the inner shell in the secondary particles.While not limiting, the ratio of the thickness of the outer shell madeof agglomerated single particles to the number average particle size ofthe secondary particles is preferably 0.1 to 0.4. At a lower thicknessratio, the zinc oxide-based particles tend to have reduced mechanicalstrength. At a higher thickness ratio, the effects expected from thedouble layer structure may not be fully produced.

The primary particles are not particularly limited in shape and size butmust be smaller than the secondary particles. For example, when thesecondary particles have a number average particle size of 0.1 to 10 μm(preferably 0.1 to 2 μm), the number average particle size of theprimary particles is 0.001 to 0.1 μm, which corresponds to {fraction(1/10)} to {fraction (1/10000)} of that of the secondary particles. Ifthe number average particle size of the primary particles is smallerthan that range, the ultraviolet screening power of the zinc oxide-basedparticles tends to be reduced. If it exceeds the above range, lighttransmitting properties tend to be reduced. If the ratio of the numberaverage particle size of the primary particles to that of the secondaryparticles is less than the above range, the UV screening power of thesecondary particles tend to be reduced. If the ratio exceeds the aboverange, the secondary particles tend to have insufficient mechanicalstrength for practical use, or the effects of agglomeration tends to beexerted unsuccessfully.

Where the secondary particles have a number of interstices among theprimary particles, and also where the secondary particles are hollow,such particles perform functions as porous fine particles ormicrocapsules. That is, they have functions of adsorption, separation,removal, and collection, such as oil absorptivity, hygroscopicity,harmful metal ion adsorptivity, harmful gas and bad order absorptivity;heat and sound insulating functions (e.g., heat insulating fillers orsound insulating fillers); a function of immobilizing metal ions,enzymes or bacteria (e.g., catalytic carriers and fillers forchromatography); light weight properties; and a function of slowlyreleasing a liquid or perfume held therein.

The zinc oxide-based particles according to embodiment (3), which arecomposite particles composed of single particles and a polymer, includethe following structures.

(3)-1: The surface of single particles is covered with a polymer. Thesingle particles do not form secondary particles or they gather onlyloosely. Those particles having an average particle size of 0.001 to0.05 μm, particularly 0.02 μm or smaller, are excellent in transparencyto the visible light and useful as a material of films screeningultraviolet rays and heat rays.

(3)-2: The single particles are agglomerated and localized to form anouter shell. In this case, the polymer can be present only in the outershell or the inner shell or both of them. It is preferable that thepolymer be present only in the outer shell and the zinc oxide-basedparticles have a hollow structure. Hollow zinc oxide-based particleshave an improved light diffusion function. While the primary particlesare not particularly limited in shape and size, they must be smallerthan the composite particles. For example, when the composite particleshave a number average particle size of 0.1 to 10 μm (preferably 0.1 to 2μm), the number average particle size of the primary particles is 0.001to 0.1 μm, which corresponds to {fraction (1/10)} to {fraction(1/10000)} of that of the composite particles. If the number averageparticle size of the primary particles is smaller than the above range,the ultraviolet screening power of the zinc oxide-based particles tendsto be reduced. If it exceeds the above range, light transmittingproperties tend to be reduced. If the ratio of the number averageparticle size of the primary particles to that of the compositeparticles is less than the above range, the UV screening power of thecomposite particles tend to be reduced. If the ratio exceeds the aboverange, the composite particles tend to have insufficient mechanicalstrength for practical use, or the effects of combination tends to beexerted unsuccessfully. Where the polymer exists in the outer shell,covering the primary particles (single particles) or the surface of thesecondary particles, the zinc oxide-based particles have excellentdispersibility and improved adhesion to a matrix polymer when formulatedinto a composition.

The polymer to be used in the zinc oxide-based particles of theinvention is not particularly limited and can be, for example, polymershaving a weight average molecular weight of 1000 to 1,000,000, includingthose generally called oligomers or prepolymers. Since such polymers areeasily dissolved or easily emulsified or suspended as finely as possiblein the first or second mixture or in the heating system forprecipitating the zinc oxide-based particles, zinc oxide-based fileparticles regular in size (a coefficient of particle size variation ofnot more than 30%) and shape can be obtained easily. The Polymer to beused in the zinc oxide-based fine particles can be, for example, atleast one resin selected from the groups (a) to (n) listed above withreference to the zinc oxide-polymer composite particles described in(10) to (19) above. When these resins are used, zinc oxide-based fineparticles having an average particle size of, e.g., 0.001 to 10 μm areobtained easily.

The process for producing the zinc oxide-based particles of theinvention is illustrated below in greater detail.

According to the process of the invention, a mixture comprising theabove-described zinc source and carboxyl-containing compound dissolvedor dispersed in an alcohol is heated at a temperature of 100° C. orhigher in the presence of a compound containing at least one elementadditive selected from the group consisting of the group IIIB metallicelements and the group IVB metallic elements (hereinafter sometimesreferred to as a metal (M)) to precipitate zinc oxide-based particlescomprising a crystalline co-precipitate of metal oxides containing 80 to99.9% of zinc and 0.1 to 20% of the metal (M) in terms of the ratio ofthe number of atoms to the total number of metallic atoms. The language“compound containing at least one element additive (M)” as used hereinis intended to mean a concept inclusive of a simple metallic body and analloy. The language will be sometimes referred to as a metal (M)compound.

The zinc source is converted to zinc oxide which is X-raycrystallographically crystalline upon being heated in a mixture of thecarboxyl-containing compound and the alcohol. The existence of the metal(M) compound in this system provides a dispersion containing the zincoxide-based particles of the invention. If any one of the threecomponents, i.e., a zinc source, a carboxyl-containing compound, and analcohol, is missing, precipitation of zinc oxide crystals does not takeplace. If the metal (M) is absent, the zinc oxide-based particles of theinvention are not obtained.

Useful zinc sources and the amount to be used and preferred examplesthereof can be those previously described with respect to the processfor producing the composite particles as described in (10) to (18)above.

Useful carboxyl-containing compounds and the amount to be used can bethose previously described with respect to the process for producingzinc oxide fine particles described in (1) to (9) above. Monocarboxylicacids described with respect to the process for producing the compositeparticles described in (10) to (18) are particularly preferred.

Useful alcohols and the amount to be used and preferred examples thereofcan be those previously described with respect to the process forproducing the composite particles as described in (10) to (18) above. Inparticular, those having a boiling point of 120° C. or higher atatmospheric pressure are preferred of them for ease of obtainingparticles of excellent crystalline properties under atmospheric pressureand in a short time. For ease of obtaining particles having excellentdispersibility, monohydric alcohols having a boiling point of 120° C. orhigher and a water solubility of not less than 1% by weight at 20° C.,for example, monoethers or monoesters of glycols and n-butanol, areespecially preferred.

The metal (M) compound which can be used in the process of the inventionis at least one compound (inclusive of a metal, such as a simple metaland an alloy) selected from, for example, metals (simple metal (M) oralloys of metal (M)); oxides; hydroxides; inorganic salts, such as(basic) carbonates, nitrates, sulfates, and halides (e.g., chlorides orfluorides); carboxylic acid salts, such as acetates, propionates,butyrates, and laurates; metal alkoxides; all the compounds containing atrivalent or tetravalent metal (M), such as metal chelate compoundsformed with a β-diketone, a hydroxycarboxylic acid, a keto ester, a ketoalcohol, an amino-alcohol, a glycol, a quinoline, etc.; and compoundscontaining a metal exhibiting a few valences, e.g., In or Tl, in thelower valent state, the metal being capable of finally changing to thetrivalent or tetravalent state in the course of fine particle formation.

In using aluminum as the group IIIB metallic element, examples ofcompounds containing aluminum are aluminum, aluminum hydroxide, aluminumoxide, aluminum chloride, aluminum fluoride, aluminum nitrate, aluminumsulfate, basic aluminum acetate, trisacetylacetonatoaluminum, aluminumtrimethoxide, aluminum triethoxide, aluminum triisopropoxide, aluminumtri-n-butoxide, an acetoalkoxyaluminum diisopropylate, aluminum laurate,aluminum stearate, diisopropoxyaluminum stearate, andethylacetoacetatoaluminum diisopropylate.

In using boron as the group IIIB metallic element, examples of compoundscontaining boron are boron trioxide, boric acid, boron bromide, borontrifluoride diethyl ether complex, boron trifluoride monoethylaminecomplex, trimethyl borate, triethyl borate, triethoxyborane, andtri-n-butyl borate.

In using gallium as the group IIIB metallic element, examples ofcompounds containing gallium are gallium, gallium hydroxide, galliumoxide, gallium(III) chloride, gallium(III) bromide, gallium(III)nitrate, gallium(III) sulfate, ammonium gallium sulfate, galliumtriethoxide, and gallium tri-n-butoxide.

In using indium as the group IIIB metallic element, examples ofcompounds containing indium are indium, indium(III) oxide, indium(III)hydroxide, indium(III) sulfate, indium(III) chloride, indium(III)fluoride, indium(III) iodide, indium isopropoxide, indium(III) acetate,indium triethoxide, and indium tri-n-butoxide.

In using thallium as the group IIIB metallic element, examples ofcompounds containing thallium are thallium, thallium(I) oxide,thallium(III) oxide, basic thallium(I) hydroxide, thallium(I) chloride,thallium(I) iodide, thallium(I) nitrate, thallium(I) sulfate,thallium(I) hydrogensulfate, basic thallium(I) sulfate, thallium(I)acetate, thallium(I) formate, thallium(I) malonate, thallium(III)chloride, thallium(III) nitrate, thallium(III) carbonate, thallium(III)sulfate, and thallium(III) hydrogensulfate.

In using silicon as the group IVB metallic element, examples ofcompounds containing silicon include silicon; silicon oxide; siliconalkoxide compounds, such as tetraalkoxysilanes (e.g.,tetramethoxysilane, tetraethoxysilane, and tetrabutoxysilane),alkylalkoxysilanes (e.g., methyltrimethoxysilane, trimethoxysilane,3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,III-glycidoxypropyltrimethoxysilane,III-(II-aminoethylaminopropyl)trimethoxysilane, diethoxydimethylsilane,trimethylethoxysilane, and hydroxyethyltriethoxysilane), and othersilane coupling agents (e.g., phenyltrimethoxysilane,benzyltriethoxysilane, γ-aminopropyltriethoxysilane,N-β(aminoethyl)γ-aminopropyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, andstearyltrimethoxysilane; chlorosilanes, such as silicon tetrachloride,trichlorosilane, and methyltrichlorosilane; and acetoxysilanes, such astriacetoxysilane.

In using germanium as the group IVB metallic element, examples ofcompounds containing germanium are germanium, germanium(IV) oxide,germanium(IV) chloride, germanium(IV) iodide, germanium(IV) acetate,germanium(IV) chloride bipyridyl complex, β-carboxyethylgermaniumsesquioxide, and germanium(IV) ethoxide.

In using tin as the group IVB metallic element, examples of compoundscontaining tin are tin, tin(IV) oxide, tin(IV) chloride, tin(IV)acetate, di-n-butyltin(IV) dichloride, di-n-butyltin(IV) dilaurate,di-n-butyltin(IV) maleate (polymer), di-n-butyltin(IV) oxide,di-n-methyltin(IV) dichloride, di-n-octyltin(IV) maleate (polymer),di-n-octyltin(IV) oxide, diphenyltin(IV) dichloride, mono-n-butyltin(IV)oxide, tetra-n-butyltin(IV), tin(II) oxalate, tri-n-butyltin(IV)acetate, tributyltin ethoxide, trimethyltin chloride, triphenyltinacetate, triphenyltin(IV) hydroxide, tin tetraethoxide, and tintetra-n-butoxide.

In using lead as the group IVB metallic element, examples of compoundscontaining lead are lead, lead(IV) acetate, lead(IV) chloride, lead(IV)fluoride, lead(IV) oxide, lead(II+IV) oxide, and lead(II) oxalate.

The oxide or hydroxide of metal (M) can be used either as powdered or inthe form of an aqueous or alcoholic sol of a metal oxide and/orhydroxide of colloidal level, such as alumina sol or silica sol.

The process of the invention comprises, for example, the following steps(I) to (III), and the metal (M) compound is added in one or more thanone of steps (I), (II), and (III).

(I) A first step of preparing a first mixture comprising a zinc sourceand a carboxyl-containing compound.

(II) A second step of mixing the first mixture with an alcohol toprepare a second mixture comprising the alcohol having dissolved ordispersed therein zinc and the carboxyl-containing compound.

(III) A third step of heating the second mixture at a temperature of100° C. or higher thereby to precipitate zinc oxide-based particlescomprising a crystalline co-precipitate of metal oxides containing 80 to99.9% of zinc and 0.1 to 20% of metal (M) in terms of the ratio of thenumber of atoms to the total number of atoms of metallic elements.

Step (I) is preferably a step of preparing a first mixture which furthercontains water. In this case, a first mixture in a solution state caneasily be obtained. The order of addition of the zinc source, thecarboxyl-containing compound, and water is arbitrary. For example, thezinc source can be dissolved in a mixed solvent of thecarboxyl-containing compound and water to prepare the first mixture.

It is preferable to carry out steps (II) and (III) by an embodiment inwhich the first mixture is added to and mixed with the alcoholmaintained at a temperature of 100° C. or higher to obtain the secondmixture with ease.

When the first mixture comprising the zinc source and thecarboxyl-containing compound, which may further comprises the metal (M)compound, is added to the alcohol, it is preferable that the firstmixture be a solution. In this case, it is desirable for the zinc sourceand the carboxyl-containing compound to be dissolved mutually or to bedissolved in a solvent having high compatibility to both of them. Water,alcohols, ketones, and esters are advantageous as such a solvent in thatthey easily dissolve the zinc source and the carboxyl-containingcompound and, if any, the metal(M) compound at a temperature of fromroom temperature up to about 100° C. and that they are also highlycompatible with the above-mentioned medium. The term “alcohols” as usedabove embraces all the alcohol species hereinabove described.

In the stage where the zinc source is converted to X-raycrystallographically crystalline zinc oxide, there are cases in whichthe reaction sometimes involves formation of one or more zinc oxideprecursors (which may or may not contain metal (M)). The case of usingzinc oxide as a zinc source may be mentioned as an example. The term“zinc oxide precursor” means ions or compounds other than zinc oxidewhich contain at least a zinc atom. For example, the precursors includea zinc (hydrate) ion (Zn²⁺), a polynuclear hydroxide ion of zinc, theabove ions partly or totally chelated by a chelating compound, e.g., aβ-dicarbonyl compound (e.g., acetylacetone), lactic acid, ethyleneglycol or ethanolamine, and (basic) carboxylic acid salts, such as(basic) zinc acetate, (basic) zinc salicylate, and (basic) zinc lactate.The precursor may be present with a part or the whole thereof forming acomposite with the carboxyl-containing compound and/or the alcohol as,for example, a complex salt.

In the stage where the zinc source and the metal (M) compound used as araw material are converted to zinc oxide-based fine particles in thesecond mixture, the carboxyl-containing compound in the second mixturedoes not change or partly or totally undergoes esterification with apart or the whole of the alcohol in the second mixture to form an estercompound.

The second mixture is not limited provided that it is a mixture obtainedby mixing the above-described four essential components, i.e., the zincsource, the carboxyl-containing compound, the alcohol, and the metal (M)compound. If desired, the mixture may contain components other than thefour components, such as water; organic solvents, e.g., ketones, esters,(cyclo)paraffins, ethers, and aromatic compounds; additives hereinafterdescribed; metallic components other than zinc and metal (M), e.g.,acetates, inorganic metal salts (e.g., a nitrate or a chloride) andorganometallic alkoxides (e.g., metal alkoxides). However, because analkali metal or alkaline earth metal sometimes causes reduction in heatray cutting function and electrical conductivity of the fine particles,its content in the mixture is preferably not more than {fraction(1/10)}, particularly not more than {fraction (1/100)}, in terms of theratio to the total number of atoms of metal (M) in the mixture. Of thesecomponents, water and organic solvents are usually used as a solventcomponent.

The mutual state of the four components and the state of each componentin the second mixture are not particularly limited. Taking the zincsource, for instance, the zinc source and/or the metal (M) compound canbe dissolved as such in a solvent component, such as the alcohol and/orwater or an organic solvent; or the zinc source is changed to theabove-described zinc oxide precursor and dissolved or dispersed in acolloidal, emulsified or suspended state in the solvent component.

Accordingly, the state of the second mixture is not particularlylimited. Whether the mixture is liquid, sol, an emulsion or a suspensionwill not cause be a problem.

The second mixture is prepared by mixing the components within theabove-described ranges. The preparation method is not particularlylimited.

In order to obtain a dispersion of zinc oxide-based particles whilecontrolling the average particle size of the single particles within arange of from 0.001 to 10 μm, it is preferred for practical productivityto add the first mixture comprising a zinc source and acarboxyl-containing compound to a heated alcohol-containing solution toprepare the second mixture.

The method of preparing the mixture according to the above-describedpreferred mode is further illustrated below.

Addition of the first mixture can be carried out by adding the wholeamount of the first mixture all at once, or adding the first mixturedropwise on or into the alcohol-containing solution, or spraying thefirst mixture.

Addition of the first mixture may be conducted at atmospheric pressure,under pressure, or under reduced pressure. Addition at atmosphericpressure is preferred from the economical consideration. In this case,when a zinc oxide-based fine particle dispersion having uniformity inparticle size and shape, etc. and a controlled state of dispersion oragglomeration is desired, it is preferable to keep thealcohol-containing solution at 60° C. or higher, particularly 60° C. to300° C., during addition and mixing. If the temperature of thealcohol-containing solution during addition and mixing is lower than 60°C., the viscosity of the second mixture tends to increase suddenlyduring or after addition and mixing, resulting in gelation. If thishappens, there arise such problems that stirring is impossible andunsuccessfully achieves uniform mixing or heat conduction in thesubsequent step, i.e., heating, is insufficient, resulting intemperature distribution. It follows that zinc oxide fine particlesuniform in crystalline properties, particle size and particle shape canhardly be obtained but agglomerated particles. This problem alsoconcerns the concentration of zinc in the second mixture and is moreliable to occur at a higher zinc concentration. The lowest suitabletemperature varies according to the pressure of the system. When themixture is prepared under reduced pressure or under pressure, thetemperature of the alcoholic solvent should be selected appropriately.When the first mixture is added to the alcohol-containing solution underheating as described above, part of the carboxyl-containing compoundand/or part of the alcohol of the second mixture are sometimes drivenout of the system through evaporation. The mixture thus prepared is alsoincluded in the second mixture.

While the raw material composition for preparing the first mixture isnot particularly limited, it is preferable that the amount of the zincsource to be used as a raw material of the first mixture ranges from 1to 90% by weight, in terms of ZnO, based on the total amount of thefirst mixture and that the amount of the carboxyl-containing compound tobe used as a raw material of the first mixture ranges from 0.5 to 50 molper mole of Zn atoms of the zinc source.

The thus prepared first mixture is added and mixed with thealcohol-containing solution to obtain the second mixture.

The first mixture when added may be at room temperature or as heated.For obtaining a uniform mixture, the alcohol-containing solution ispreferably stirred while the first mixture is being added thereto.

While not limiting, the amount of the alcohol in the alcohol-containingsolution preferably ranges from 1 to 100 mol per mole of the Zn atomsoriginated in the zinc source present in the second mixture so that theformation of zinc oxide-based fine particles under heating may becompleted in a short time period. The alcohol concentration in thealcohol-containing solution is usually in a range of from 5 to 100% byweight based on the total weight of the solution.

Heating of the thus prepared second mixture results in production of adispersion containing zinc oxide-based particles in good yield.

The heating temperature is not particularly limited. The heating mustbe, as a matter of course, at or above the temperature at whichcrystalline zinc oxide precipitates, but the temperature cannot bedecided definitely because it is subject to variation in accordance withdesired morphology of zinc oxide-based fine particles, such as the size,shape and state of dispersion or agglomeration. The heating temperatureand heating time should be selected from a comprehensive point of viewincluding the initial composition of the second mixture and theabove-mentioned various parameters. In particular, when it is desired toobtain a dispersion of zinc oxide-based fine particles having theaverage single particle size controlled within a range of from 0.001 to10 μm with practical productivity, it is preferable to heat the secondmixture at 100° C. or higher, still preferably 100 to 300° C.,particularly preferably 120° C. or higher.

In the case when the first mixture is added to an alcohol-containingsolution kept at 100° C. or higher to obtain the second mixture, heatingof the resulting second mixture can be achieved by maintaining themixture at that temperature, or the mixture is heated or cooled to aprescribed temperature, followed by heat treatment. In the case when thefirst mixture is added to an alcohol-containing solution below 100° C.to obtain the second mixture, the resulting second mixture is heated to100° C. or higher, followed by heat treatment. To set the second mixtureheating temperature at 100° C. or higher brings about the advantage thatstrict control on the composition of the reaction system, inclusive ofcontrol on the rate of evaporation of excessive or unnecessarycomponents and the amount of the evaporated components, can be takeneasily for obtaining zinc oxide-based fine particles. As a result, theparticle size and the like of the resulting particles can be controlledeasily.

In the heating step for obtaining the dispersion, the components otherthan the above-described ones, i.e., the alcohol, the aforesaid estercompound produced upon heating, or the solvent component which may, ifdesired, have been used in the mixture may be removed by evaporationpartially or completely.

While not limiting, a preferred heating time for completion of thereaction is usually about 0.1 to 30 hours.

Where water is present in the second mixture, it is preferable forconversion to zinc oxide-based fine particles to evaporate the water toreduce the free water content of the dispersion to 5% by weight orlower, particularly 1% by weight or lower, during the heating step. Ifthe water content exceeds the above level, cases are sometimes met withthat the zinc oxide-based fine particles have reduced crystallineproperties, resulting in a failure of fulfilling the function of zincoxide, while such depends on the kinds of the other components presentin the dispersion, such as the alcohol.

It is preferable that the amount of the carboxyl-containing compound ina finally obtained zinc oxide-based particle dispersion be 0.5 mol orless per mole of the total zinc atoms present in the dispersion. If itexceeds 0.5 mol, there are sometimes cases in which the zinc oxide-basedfine particles have reduced crystalline properties, failing to fulfillthe function of zinc oxide. Accordingly, where the amount of thecarboxyl-containing compound present in the second mixture is such thatthe amount of the carboxyl-containing compound in the finally obtaineddispersion will exceed 0.5 mol per mole of the total zinc atoms in theresulting dispersion, at least the excess should be removed byevaporation during the heating step. Needless to say, thecarboxyl-containing compound may be evaporated during heating even ifthe above molar ratio is 0.5 or lower.

The process of maintaining the system at 100° C. or higher in thepresence of lactic acid or a compound thereof is effective in obtainingsecondary particles that are agglomerates of the above-identified singleparticles as primary particles. Lactic acid or a compound thereof to beused includes lactic acid; lactic acid metal salts, such as ammoniumlactate, sodium lactate, lithium lactate, calcium lactate, magnesiumlactate, zinc lactate, aluminum lactate, manganese lactate, ironlactate, nickel lactate, and silver lactate; and lactic ester compoundscapable of generating lactic acid on hydrolysis, etc., such as methyllactate, ethyl lactate, and n-butyl lactate. These compounds may be usedeither individually or as a combination of two or more thereof.

While not limiting, the amount of lactic acid or a compound thereof isusually 0.001 to 0.4 in terms of molar ratio to zinc in the secondmixture. At a lower molar ratio, the effect of the presence of lacticacid tends to be insufficient for obtaining zinc oxide crystals. At ahigher molar ratio, precipitation reaction of zinc oxide crystals tendsto hardly take place, failing to obtain desired fine particles. In orderto obtain fine particles regular in shape, the molar ratio of lacticacid to zinc is preferably in the range of from 0.001 to 0.2. In orderto obtain fine particles regular in size and having satisfactorydispersibility, the molar ratio of lactic acid to zinc is preferably inthe range of from 0.001 to 0.1.

Addition of lactic acid or a compound thereof can be carried out, forexample, as follows. In using lactic acid (CH₃CH(OH)COOH) and/or alactic ester, it can be added at any stage from step (I) through step(III) either directly or as dissolved in a solvent (e.g., an alcohol).The latter manner of addition is preferred for smooth spread of thelactic acid particularly when a lactic acid source is added in step(III). In using a metal lactate, it can be added at any stage from step(I) through step (III), and preferably it is dissolved in the firstmixture together with the zinc source or in the form of a zinc source instep (I). For example, a zinc source powder and a metal lactate powderare mixed with a solution containing a monocarboxylic acid and stirredto form a uniform solution. In this preparation, stirring while heatingis preferred for increasing the rate of dissolution and solubility ofeach powder thereby to provide a high concentration solution in a shorttime.

Where lactic acid is dissolved or dispersed in the medium, casessometimes occur in which zinc oxide crystals grow anisotropically intothin plate like zinc oxide crystals to provide a dispersion containingzinc oxide-based fine particles whose surface comprises a cluster ofsuch thin plate like zinc oxide crystals with their tips projectingoutward. In such cases and when the lactic acid to zinc molar ratiofalls within a range of from 0.001 to 0.4, there are formed favorablesingle particles having a thin plate shape (anisotropic shape) whichhave, for example, an L/B ratio (major axis/minor axis) of 1.0 to 5.0, aflatness (major axis/thickness) of 2 to 200, and a major axis of 5 to1000 nm, and exhibit excellent diffused transmission properties. Themajor axis is the longest of measured three axes of the particle, andthe thickness is the smaller of the width and the height out of thethree axes.

The polymer which can be used in the process of the invention are thesame as those explained with regard to the zinc oxide-based particles ofthe invention.

While not limiting, the polymer is used at a weight ratio of, forexample, 0.01 to 2.0, to the zinc atoms, as converted to zinc oxide, inthe zinc source (of the second mixture). If the amount of the polymer islower than that ratio, composite particles tend to be hardly obtained.If the amount of the polymer is higher than that ratio, theprecipitation of zinc oxide crystals tends to hardly occur. In order toobtain zinc oxide-based particles having the above-mentioned doublelayer structure, uniformity in particle shape and size, and satisfactorydispersibility, the polymer is preferably used at a weight ratio of 0.05to 0.5 to the zinc oxide content, while somewhat varying according tothe kind of the polymer and other reaction conditions.

According to the process of the invention, the polymer is added to anyone or more than one steps of the above-described steps. Addition of thepolymer is conducted at an arbitrary stage before precipitation of zincoxide-based particles. For example, the polymer can be added to thefirst mixture or the second mixture.

According to the process of the invention, the polymer can be added inany of the above-described steps but before formation of zincoxide-based particles.

For smooth spread of the polymer throughout the reaction system, it ispreferable for the polymer to be previously dissolved in the samealcohol as used as a medium or an arbitrary solvent. The solvent fordissolving the polymer is not particularly limited as far as it iscapable of dissolving the polymer, and is usually at least one memberselected from organic solvents, such as alcohols (the above-describedones), aliphatic or aromatic carboxylic acids, aliphatic or aromaticcarboxylic acid esters, ketones, ethers, ether esters, aliphatic oraromatic hydrocarbons, and halogenated hydrocarbons; water; mineral oil;vegetable oil; wax oil; and silicone oil.

The second mixture is not limited provided that it is a mixture obtainedby mixing the above-described four essential components, i.e., a zincsource, a carboxyl-containing compound, an alcohol, and metal (M). Inorder to obtain hollow particles the outer shell of which is formed ofco-precipitated single particles or particles comprising a polymerhaving dispersed therein a number of single particles, the polymer isadded in a stage before formation of zinc oxide-based particles.

On maintaining the second mixture containing the polymer at 100° C. orhigher, preferably 100 to 300° C., still preferably 150 to 200° C., fora period of 0.1 to 30 hours, preferably 0.5 to 10 hours, there areobtained the zinc oxide-based particles of the invention as zincoxide-based crystals-polymer composite particles with practicalproductivity in accordance with the kinds and ratios of the rawmaterials. That is, on maintaining the second mixture at a temperaturewithin the above range for a period within the above range, the zincdissolved or dispersed in the medium is converted to X-raycrystallographically crystalline zinc oxide. Because the medium also hasdissolved or dispersed therein the polymer, the polymer forms acomposite while the nuclei of zinc oxide crystals precipitate and grow,thereby providing a dispersion containing zinc oxide-polymer compositeparticles. The internal structure, shape and size of the compositeparticles formed, and the particle size of the single particles(co-precipitated metal oxide) present therein can be controlled byselection of the kinds and ratios of the raw materials (e.g., thepolymer and the alcohol), the composition and temperature of thereaction system at the time when composite particles are formed that arebased on the thermal history, etc. applied till composite particles areformed.

According to the process of the invention, there is obtained adispersion containing 1 to 80% by weight of zinc oxide-based particlesin an alcohol and/or the above-described ester compound and/or anorganic solvent, in which the zinc oxide-based particles contain a metaloxide co-precipitate and a polymer and have a number average particlesize of 0.001 to 10 μm and a coefficient of size variation of not morethan 30%.

It is also possible to add a specific additive to the system in the stepof heating for the purpose of controlling the size, shape, state ofdispersion or higher-order and/or the polarity or composition of thesurface of the finally obtained zinc oxide-based single particles. Thestage of addition of the additive is not particularly restricted. Theadditive can be added in either of the step of preparing the secondmixture or the first mixture or the step of heating. The stage ofaddition is selected appropriately according to the purpose and the kindof the additive. In many cases, the effects of the additive are fullyexerted when added immediately before or after precipitation of zincoxide crystals.

In particular, in order to obtain zinc oxide-based particles having highuniformity in size and shape of the single particles, it is preferablethat a compound containing in the molecule thereof a carboxyl group, anamino group, a quaternary ammonio group, an amido group, an imido bond,a hydroxyl group, an ester bond, a urethane group, a urethane bond, aureido group, a ureylene bond, an isocyanate group, an epoxy group, aphosphoric acid group, a metallic hydroxyl group, a metallic alkoxygroup, and a sulfonic acid group and having a molecular weight of lessthan 1,000 be present as an additive in the system in the heating step.

Useful additives and their amount can be those described with referenceto the process for producing the zinc oxide fine particles described in(1) to (9) above.

A preferred embodiment of the invention for obtaining zinc oxide-basedparticles having an average single particle size controlled within arange of from 0.001 to 0.1 μm can be achieved when any one of thefollowing conditions (I) to (IV), preferably 2 or 3 of the conditions,still preferably all of them are satisfied.

(I) Of the above-described zinc sources, a zinc source mainly comprisingat least one compound selected form the group consisting of zinc oxide,zinc hydroxide, and zinc acetate, particularly a zinc source mainlycomprising zinc oxide and/or zinc hydroxide is used.

Zinc oxide, zinc hydroxide, and zinc acetate contain substantially noimpurity that might interfere with the reaction forming zinc oxide-basedfine particles in the heating step, therefore making it easy to strictlycontrol the particle size to such fineness of 0.001 to 0.1 μm. Aboveall, zinc oxide and zinc hydroxide are available at a low price, allow afree choice of the carboxyl-containing compound to be combined with, andmake it particularly easy to obtain fine particles within the aboveparticle size range.

(II) The carboxyl-containing compound is a saturated fatty acid having aboiling point of 200° C. or lower at atmospheric pressure.

Specifically, formic acid, acetic acid, propionic acid, butyric acid,and isobutyric acid are preferred. Acetic acid is particularlypreferred. With these compounds, it is easy to control the carboxylgroup content in the reaction system from mixing through heating, thusmaking it easy to strictly control the particle size to such fineness.It is still preferable to use the above saturated fatty acid in aproportion of 80 mol % or higher in the total carboxyl-containingcompounds.

While the content of the carboxyl-containing compound falling within theabove-described preferred range is not limited further, a particularlypreferred content of the carboxyl-containing compound in the firstmixture ranges from 2.2 to 10 mol per mole of Zn atoms of the zinc oxidefor obtaining fine particles which have excellent dispersibility andprevented from secondary agglomeration.

(III) The second mixture is prepared by adding the first mixture,obtained by mixing a zinc source, a carboxyl-containing compound, and ametal (M) compound, to an alcohol-containing solution kept at 100° C. orabove, particularly 1000 to 300° C., by continuous or intermittentdropwise addition.

The first mixture is preferably in a liquid state. It is stillpreferable that the zinc source, the carboxyl-containing compound, andthe metal (M) compound are mutually dissolved or they are dissolved in asolvent having high compatibility with them. Water, alcohols, ketones,and esters are advantageous as such a solvent in that they easilydissolve the zinc source and the carboxyl-containing compound underheating at room temperature up to about 100° C. and that they are alsohighly compatible with the alcoholic solvent. The term “alcohols” asused above embraces all the alcohol species described above.

(IV) The heating of the second mixture is conducted at 1000 to 300° C.,particularly 1500 to 300° C.

At the time when ZnO crystals precipitate to form the particles of theinvention on heating the second mixture, the Zn concentration in termsof ZnO in the second mixture is preferably 0.5 to 20 wt %, stillpreferably 2.0 wt % or higher and lower than 10 wt %, for obtainingparticles which have an average primary particle size of 0.001 to 0.1 μmand are prevented from secondary agglomeration.

The zinc oxide-based particles having an average particle size rangingfrom 0.001 to 0.1 μm can be made those with further controlleduniformity in size and shape, controlled surface conditions, such ashydrophilic/lipophilic properties, or a controlled state of dispersionor agglomeration. Effective methods for controlling these attributes areset forth below. In the preferred process for producing zinc oxide-basedparticles having an average particle size of 0.001 to 0.1 μm, additionof the above-described additive in the same manner as described above isalso effective in obtaining zinc oxide-based particles with a controlledshape, a controlled state of dispersion or higher-order structure, andcontrolled surface polarity. When it is desired to produce zincoxide-based particles which have a regular primary particle sizedistribution with the average particle size substantially falling withinthe above range, and are inhibited from secondary agglomeration, it ispreferable to use a zinc source comprising, as a main component, atleast one compound selected from the group consisting of zinc oxide,zinc hydroxide, and zinc acetate and, as a secondary component, basiczinc carbonate and/or a zinc salt of a carboxyl-containing compoundhaving a boiling point higher than the heating temperature atatmospheric pressure. The ratio of the secondary component to the maincomponent is 0.01 to 20% in terms of atomic ratio of zinc. If the ratiois less than 0.01%, the effect of the combined use of the secondarycomponent is insufficient. If it exceeds 20%, the system sometimes failsto produce zinc oxide having high crystalline properties.

As an alternative process for obtaining zinc oxide-based particlesregular in shape and size and excellent in dispersibility, it iseffective to perform the heat treatment in the presence of carbonateions and/or CO₂. This can be achieved by, for example, supplying carbondioxide gas intermittently or continuously or adding a compound capableof generating carbon dioxide or carbonate ions under heating, such asurea, ammonium (hydrogen)carbonate, and basic zinc carbonate, to theheating system before and/or during the zinc oxide forming reaction.

When the above-described conditions are satisfied in the process of theinvention, there is obtained a dispersion containing zinc oxide-basedparticles in a zinc oxide concentration of 1 to 80% by weight in analcohol and/or the above-described ester compound and/or an organicsolvent, in which the particles have an average particle size of 0.001to 0.1 μm, a controlled shape, a controlled surface condition, and acontrolled state of dispersion or agglomeration.

The dispersion of the zinc oxide-based particles obtained in theinvention can be used as such. If desired, the dispersion can easily bepowdered or transformed to a coating composition containing the zincoxide-based particles or a dispersion of the zinc oxide-based particlesin a different medium (by solvent substitution).

Powdering or solvent substitution can be carried out in the same manneras described with reference to the process for producing the compositeparticles as described in (10) to

Use of the zinc oxide fine particles obtained by the process describedin (1) to (9), the zinc oxide-polymer composite particles obtained bythe process described in (10) to (18), the inorganic compound particlesobtained by the process described in (19) to (26), the zinc oxide-basedparticles obtained by the process described in (27) to (36), the zincoxide-polymer composite particles described in (37) to (42), theinorganic compound particles described in (43) to (49), and the zincoxide-based particles described in (50) to (58) (hereinafter inclusivelyreferred to as “zinc oxide-based fine particles”) will be describedbelow.

The zinc oxide-based fine particles according to the invention can beused in the form of a composition containing at least one of them invarious industries. For the purpose of adding value to films, sheets,fiber, plastic plates, glass, paper, cosmetics, and so on, at least onekind of the zinc oxide-based fine particles of the invention is added toresin compositions providing films, sheets, fiber, plastic plates,paper, cosmetics, etc.; coating compositions to be applied to films,sheets, fiber, plastic plates, etc.; paper; cosmetics; and the like.

[1] Coating Composition and Coated Articles of the Invention

The coating composition of the invention contains at least one kind ofparticles selected from the zinc oxide-based fine particles of theinvention and a binder component capable of forming a coating filmbinding the zinc oxide-based fine particles. The zinc oxide-based fineparticles and the binder component are used in an amount of 0.1 to 99%by weight and 1 to 99.9% by weight, respectively, based on the totalsolids content of them.

The coated article according to the invention comprises at least onesubstrate selected from the group consisting of a resin molded article,glass, and paper and a coating film provided on either one or both sidesof the surface of the substrate. The coating film comprises at least onekind of the zinc oxide-based fine particles of the invention and abinder component binding the zinc oxide-based fine particles. The amountof zinc oxide-based fine particles and the binder component is 0.1 to99% by weight and 1 to 99.9% by weight, respectively, based on theirtotal solids content. The resin molded article as a substrate has atleast one form selected from the group consisting of a plate, a sheet, afilm, and fiber. The substrate may be either transparent orsemitransparent.

If the amount of the fine particles exceeds the above range, the coatingfilm has insufficient adhesion to the substrate, poor scratch resistanceor abrasion resistance. If it is lower than that range, the effects ofadding the fine particles are insufficient.

The total weight of the zinc oxide-based fine particles and the bindercomponent is, for example, 1 to 80% based on the weight of the coatingcomposition, being selected appropriately according to the purpose ofuse, workability, and the like. The balance of the coating compositioncomprises a solvent for dispersing the fine particles and for dissolvingor dispersing the binder component and additives used according to theuse of the composition, such as pigments.

The binder component useful in the coating composition is notparticularly limited and includes (1) organic binders, such asthermoplastic or thermosetting synthetic resins, e.g., (meth)acrylicresins, vinyl chloride resins, silicone resins, melamine resins,urethane resins, styrene resins, alkyd resins, phenolic resins, epoxyreins, and polyester resins, and synthetic or natural rubbers, e.g.,ethylene-propylene copolymer rubber, polybutadiene rubber,styrene-butadiene rubber, and acrylonitrile-butadiene rubber; and (2)inorganic binders, such as silica sol, alkali silicates, siliconalkoxides, and phosphates. These binder components are used eitherindividually or as a combination of two or more thereof, being selectedappropriately according to the requirements of the coating film formedby applying the coating composition onto a substrate and drying, such asheat resistance and scratch resistance, or the kind of the substrate.

The binder component may be used as dissolved, emulsified or suspendedin a solvent.

The solvent for the binder component is selected appropriately accordingto the use of the coating composition and the kind of the binder.Examples of useful solvents include organic solvents, such as alcohols,aliphatic or aromatic carboxylic acid esters, ketones, ethers, etheresters, aliphatic or aromatic hydrocarbons, and halogenatedhydrocarbons; water; mineral oil, vegetable oil, wax oil and siliconeoil. Suitable solvents are selected according to the use. If desired,two or more of these solvents may be used as a mixture at an arbitraryratio. The solvent for the binder component can be the solvent of thedispersion of the particles according to the invention.

The method of preparing the coating composition is not particularlylimited. For example, the powder of the fine particles is dispersed in asolvent containing the binder component; a dispersion of the fineparticles in a solvent and a solvent containing the binder component aremixed; or the binder component is added to a dispersion of the fineparticles in a solvent. The dispersing method is not limited, and knowntechniques using, for example, a stirrer, a ball mill, a sand mill or anultrasonic homogenizer can be applied.

The coating composition of the invention can also be obtained by addingthe binder component or a solvent containing the binder componentdirectly to the dispersion of zinc oxide-based particles as produced bythe above-described processes.

The coating composition obtained by the above-described methods containsat least the fine particles, the binder component, and the solvent.

The resulting coating composition is applied to an arbitrary substrateand dried to provide a film containing the zinc oxide-based particles.The substrate includes plastic films or sheets, such as a polyesterfilm; fiber, such as natural fiber or synthetic fiber; transparent orsemitransparent synthetic resin plates made of, e.g., vinyl chlorideresins, polycarbonate resins, acrylic resins, and a polyethyleneterephthalate resin; glass; and paper.

If necessary, the coating film may be heated at a temperature below thedeformation temperature of the substrate for the following purposes. Toaccelerate condensation reaction among the molecules of an inorganicbinder component, e.g., a silicon alkoxide, thereby to form a toughfilm; to accelerate curing reaction of a thermosetting resin as a bindercomponent, thereby to provide a cured film; and to help efficientprogress of crosslinking reaction between a resin having two or moreactive hydrogen atoms, such as polyether and/or polyester, which is usedas at least part of the binder component, and a crosslinking agent, suchas an isocyanate compound, thereby to form a polyurethane film.

The coated film of the coated article of the invention is a film formedon drying or dry-curing (dry-crosslinking) the above-mentioned organicand/or inorganic binder.

The method of applying the coating composition of the invention is notparticularly limited, and any known coating technique, such as dipping,spraying, screen printing, roll coating, and flow coating, can be used.

The coating film thus formed of the coating composition of the inventionand the resulting coated articles of the invention comprises the bindercomponent having dispersed therein the zinc oxide-based fine particlesof the invention. Therefore, the coating film and the coated articleexhibit the functions reflecting the characteristics possessed by thefine particles. That is, they have (a) UV-cutting power. Where the zincoxide-based particles obtained by the process described in (27) to (36)or the zinc oxide-based particles described in (50) to (58) are used,the coating film and the coated article additionally have (b) infrared(IR; inclusive of near infrared rays (=heat rays) and far infraredrays)-cutting power and (c) controlled electrical conductivity. Whereultrafine particles are used, the coating film is excellent in visiblelight transmitting properties (=transparency). Where fine particleshaving a double layer structure, such as hollow particles, are used, thecoating film is excellent in light scattering properties.

Since the zinc oxide-based fine particles of the invention mainlycomprise ZnO, they have excellent antimicrobial properties, therebyproviding coated articles having an antimicrobial action.

When all the fine particles in the coating composition are regular inshape and have a number average particle size of 0.1 to 10 μm with acoefficient of size variation of not more than 30%, the resulting coatedfilm and the coated article exhibit at least the characteristics (a) to(c) and, in addition, slip properties and anti-blocking properties whileretaining surface flatness.

[2] Resin Composition and Resin Molded Articles of the Invention

The resin composition according to the invention comprises at least onekind of the zinc oxide-based fine particles of the invention and a resincapable of forming a continuous phase in which the zinc oxide-based fineparticles are dispersed. The amount of zinc oxide-based fine particlesand the resin is 0.1 to 99% by weight and 1 to 99.9% by weight,respectively, based on their total solids content.

If the amount of the fine particles is larger than the above range, theresulting molded article tends to have insufficient mechanical strength.If the amount is smaller than the above range, the effects of the fineparticles may not be exerted fully.

The resin molded article of the invention is an article obtained bymolding the resin composition of the invention into a shape selectedfrom the group consisting of a plate, a sheet, a film, and fiber.

The resin used in the resin composition and the resin molded article isnot particularly limited in kind and is selected appropriately accordingto the end use. Illustrative examples of useful resins are (1)thermoplastic or thermosetting resins, such as polyolefin resins (e.g.,polyethylene and polypropylene), polystyrene resins, vinyl chlorideresins, vinylidene chloride resins, polyvinyl alcohol, polyester resins(e.g., polyethylene terephthalate and polyethylene naphthalate),polyamide resins, polyimide resins, (meth)acrylic resins (e.g.,polymethyl (meth)acrylate), phenolic resins, urea resins, melamineresins, unsaturated polyester resins, polycarbonate resins, and epoxyresins, and (2) natural or synthetic rubbers, such as ethylene-propylenecopolymer rubber, polybutadiene rubber, styrene-butadiene rubber, andacrylonitrile-butadiene rubber. These resins are used eitherindividually or as a combination of two or more thereof.

The process for preparing the resin composition of the invention is notparticularly limited, and the resin composition can be obtained bymixing and dispersing the fine particles of the invention in the resin.For example, the resin composition can be obtained by a conventionallyknown process, such as a masterbatching process, in which powder of thefine particles is added to the melt-kneading system of a pelletized orpowdered resin, or a process comprising dispersive mixing of the fineparticles in a resin solution followed by solvent removal.Alternatively, a process comprising dispersive mixing of the fineparticles in the course of resin preparation can also be adopted. In thecase of using polyester, for instance, powder of the fine particles,preferably a dispersion of the fine particles in the glycol componentused as a starting material of the polyester, is added to the polyesterpreparation system at any stage of from interesterification throughpolymerization.

According to the above-described processes, there is obtained a resincomposition comprising the resin having dispersed therein the fineparticles of the invention. The resin composition can be formed into ageneral molding compound, such as pellets. On molding, the resincomposition provides a molded article in the form of a plate, a sheet, afilm, fiber, etc. which contains the fine particles of the invention andexhibits UV-cutting power. Where the zinc oxide-based particles obtainedby the process described in (27) to (36) and the zinc oxide-basedparticles described in (50) to (58) are used, the molded articleadditionally has IR (inclusive of near infrared rays (=heat rays) andfar infrared ryas)-cutting power and controlled electrical conductivity.Where ultrafine particles are used, it has excellent visible lighttransmitting properties (=transparency). Where fine particles having adouble layer structure, such as hollow particles, are used, the moldedarticle is excellent in light scattering properties.

Since the zinc oxide-based particles of the invention mainly compriseZnO, they have excellent antimicrobial properties, thereby providingmolded articles having an antimicrobial action.

When all the fine particles in the resin composition are regular inshape and have a number average particle size of 0.1 to 10 μm with acoefficient of size variation of not more than 30%, the resulting resinmolded article exhibits slip properties and anti-blocking propertieswhile retaining surface flatness. The molded article in film form,particularly an oriented film obtained by stretching the molded film hassurface unevenness ascribed to the presence of the fine particles. Inusing the fine particles obtained in accordance with preferredembodiments of the invention, i.e., the particles regular in size andhighly dispersed, the film has uniform and fine surface unevenness andexcellent slip properties or anti-blocking properties while retainingextremely high flatness. For example, polyester films obtained in thisway are useful as a base of magnetic tapes, wrap film or a film of acondenser.

The process of obtaining a molded article in a desired shape from theresin composition of the invention is not particularly limited, andconventional molding techniques can be adopted as they are. Illustrativeexamples of molding are shown below.

In the production of a polycarbonate resin plate containing the fineparticles of the invention, pellets or powder of a polycarbonate resinand powder of a prescribed amount of the fine particles are melt kneadedto prepare a composition in which the fine particles are uniformlydispersed in the resin. The composition, either as it is or afterpelletized, is then molded by injection molding, extrusion, compressionmolding, and the like into a flat or curved plate shape. As a matter ofcourse, the resulting plate-shaped article can further be subjected topost processing into an arbitrary shape, such as a wavy plate shape.Plates of other resins, such as acrylic resins, vinyl chloride resins,and polyester resins, can also be obtained similarly.

In the production of fibers (e.g., nylon fiber and polyester fiber) orfilms (e.g., a polyolefin film, a polyamide film or a polyester film)containing the fine particles of the invention, powder of the fineparticles and pellets or powder of a resin are melt kneaded to prepare acomposition in which the fine particles are uniformly dispersed in theresin. The composition, either as it is or after pelletized, is thenmolded into fiber by a conventional technique, such as melt spinning, orsheeted by a conventional sheeting technique, such as extrusion into asheet, which is, if necessary, uniaxially or biaxially stretched then.

The resin molded article of the invention includes laminated films orsheets comprising one or more layers containing the fine particles ofthe invention, which can be used as wrap film for food, etc., heatinsulating film, gas barrier film, and the like. The laminated films orsheets can be produced by, for example, a process of laminating a filmor sheet containing the fine particles of the invention with other filmsor sheets by heat fusion or via an adhesive (or an adhesive layer) or aprocess of coating a film or sheet with the above-described coatingcomposition of the invention. Further, a laminated film or sheet can beproduced by co-extruding (1) a composition of powder of the fineparticles of the invention and resin pellets or powder or (2) resinpellets or powder previously containing the fine particles of theinvention onto a base film or sheet or any functional film or sheet.Apparatus used therefor can be a conventional film extruder used forproduction of a multi-layer film or sheet.

Polyester fiber or polyester film having dispersed therein the fineparticles of the invention can also be produced by the followingconventional process.

Polyester fiber can be obtained by adding a dispersion of the fineparticles, for example, a 0.1 to 50 wt % dispersion in a glycolcomponent, to the polyester preparation system at any stage of frominteresterification through polymerization, followed by completion ofthe polymerization reaction to obtain a polyester resin having dispersedtherein the fine particles and melt spinning the resulting polyesterresin in a conventional manner.

A polyester film can be obtained by preparing a polyester resin havingdispersed therein the fine particles in the same manner as describedabove and extruding the resin into a sheet. If desired, the extrudedsheet is stretched uniaxially or biaxially.

[3] Paper of the Invention

Paper according to the invention comprises pulp made into paper and atleast one kind of the zinc oxide-based fine particles of the inventiondispersed in the pulp. The amount of the zinc oxide-based fine particlesis 0.01 to 50% by weight, preferably 0.1 to 20% by weight, based on thepulp. If the amount of the particles is smaller than 0.01%, the effectsof addition of the fine particles are insufficient. If it exceeds 50%,the paper has reduced mechanical characteristics.

The paper as referred to herein is not restricted as far as it containsthe fine particles of the invention and includes, for example,self-containing paper, coated paper, impregnated paper, and processedpaper, such as film-laminated paper.

The terminology “self-containing paper” means paper having the fineparticles dispersed in the inside thereof and/or on the outer surfacethereof, which is obtained by adding the fine particles in an arbitrarystage of from beating of pulp through paper making. The manner ofaddition of the fine particles is not particularly limited. The fineparticles are usually added in powder form or as dispersed in, e.g.,water. The steps involved up to paper making and drying are carried outin accordance with conventionally known paper making techniques.Conventionally known raw materials can be used in the invention. Forexample, pulp is beaten by means of a pulper, etc. to prepare a pulpslurry, and an aqueous dispersion of the fine particles of the inventionis added to the slurry. The pulp slurry is then made into paper anddried to obtain paper having dispersed therein the fine particles. Ifdesired, a sizing agent, ammonium sulfate, a strengthening agent, etc.can be added in an arbitrary stage.

Coated paper is paper obtained by applying a coating compositioncontaining the fine particles of the invention to a paper base anddrying to form a coating film containing the fine particles. Impregnatedpaper is paper having the fine particles adhered on one or both sidesthereof, which is obtained by impregnating a paper base with adispersion of the fine particles in an aqueous or organic medium whichmay contain a binder, followed by drying.

Preparation of the coated paper and the impregnated paper is notparticularly restricted, and any known coating or impregnation techniquecan be applied, using paper prepared by a general paper making processas a base, except for using the fine particles of the invention.

The fine particles-containing coating composition or dispersion to beused are prepared in a conventional manner using conventional rawmaterials, and the solvent or the binder to be used can be thoseconventionally employed.

The content of the fine particles in the coating composition or thedispersion is not further limited as long as it is within a range offrom 0.1 to 100% by weight based on the solids content, and is decidedappropriately according to the use, and the like.

The term “solids content” as used above means the total weight of thefine particles of the invention and a binder in the coating compositionor the dispersion. The coating composition used for producing coatedpaper can be the one that is included in the above-described coatingcompositions according to the invention and contains a solvent. Thedispersion medium of the dispersion used for producing coated paper canbe the solvent usable in the above-described coating compositions of theinvention. The coating composition may further contain additives, suchas pigments, water repellents, lubricants, defoaming agents, fluiditymodifiers, and water retaining agents, in addition to theabove-described components in accordance with the purpose of use.

Film-laminated paper is paper composed of a paper base and a highpolymer film bonded thereto, the high polymer film having dispersedtherein the fine particles obtained by the above-described processes.The high polymer film can be the above-described resin molded articleaccording to the invention.

The paper containing the fine particles of the invention which can beobtained by the above-mentioned processes is useful as paper withexcellent appearance. The use of the resulting paper is arbitrary, andthe paper finds a variety of applications as, for example, art paper orwall paper.

When all the fine particles contained in the paper are regular in shapeand have a number average particle size of 0.1 to 10 μm with acoefficient of size variation of not more than 30%, preferably a numberaverage particle size of 0.1 to 2 μm with a coefficient of sizevariation of not more than 15%, the paper possesses excellent surfaceflatness not heretofore attained and improved printability.

[4] Cosmetics of the Invention

The cosmetics according to the invention contain at least one kind ofthe zinc oxide-based fine particles of the invention in an amount of0.1% by weight or more. The amount of the zinc oxide-based fineparticles is usually from 0.1 to 50% by weight based on the total solidscontent of the cosmetics. As far as the effects of the invention are notimpaired, the cosmetics contain other components commonly used incosmetics in addition to the above essential component according to thepurpose. For example, (1) one or more of oils, such as liquid fats andoils, solid fats and oils, waxes, and hydrocarbons, and polyhydricalcohols, such as polyethylene glycol and propylene glycol, and (2) oneor more of surface active agents, thickeners, perfumes, drugs,antioxidants, chelating agents, coloring matter, water, antiseptics,antifungals, and the like can be added. Further, (3) one or morepigments selected from extender pigments, such as kaolin, talc, andmica, inorganic pigments, such as an iron oxide pigment and a TiO₂pigment, and organic pigments, such as red #202 and yellow #4 and/or (4)one or more of organic UV absorbers, such as benzoic acid type, cinnamicacid type, salicylic acid type or benzophenone type UV absorbers canalso be used in combination with the fine particles of the invention.

The cosmetics of the invention are superior cosmetics that can screenout ultraviolet light and are also excellent in antimicrobial propertiesand deodorizing properties. The purpose of incorporating the fineparticles into the cosmetics includes anti-sunburn, furnishingantimicrobial activity, and furnishing deodorizing properties, varyingdepending on the composition, morphology, particle size, etc. of thefine particles used. For example, addition of the zinc oxide-basedparticles obtained by the process described in (27) to (36) or the zincoxide-based particles described in (50) to (58) produces an effect ofscreening heat rays. Addition of the zinc oxide-polymer compositeparticles obtained by the process described in (10) to (18) or the zincoxide-polymer composite particles described in (37) to (42) gives aneffect of improving smoothness. Addition of hollow particles affords aneffect of improving transparency, and addition of porous particlesbrings about an effect of improving moisture retention.

The use of the cosmetics of the invention is not particularly limited.The forms the cosmetics can take include powdery, creamy or oilyfoundation; skin-care cosmetics, such as clear lotion, emulsion, beautyoil, and cream; and makeup cosmetics, such as lipstick and eye shadow.

The cosmetics of the invention are not further limited in composition asfar as the fine particles are contained, comprising a conventionalcosmetic composition having incorporated therein the fine particles.Accordingly, raw materials generally used in cosmetics can be used assuch.

Accordingly, the process for producing the cosmetics of the invention isnot particularly limited provided that a requisite amount of the fineparticles is added and dispersed in any arbitrary stage of conventionalpreparation of a cosmetic composition according to the use or kind ofthe cosmetics. Since the fine particles of the invention are hardlyagglomerated and easily dispersible in general cosmetic compositions, adispersive mixing method commonly used for powdery materials ofcosmetics can be applied to provide cosmetics in which the fineparticles are highly dispersed. The fine particles may be added as suchor, if desired, can be subjected to a surface treatment commonlyemployed for powdery cosmetic materials for rendering lipophilic orhydrophilic, for example, a treatment with an anionic, cationic,nonionic or amphoteric surface active agent, a metallic soap, silicone,etc. The surface treatment may be conducted either before or during theaddition and mixing.

The cosmetics of the invention have at least UV-cutting power.Additionally, when the zinc oxide-based particles obtained by theprocess described in (27) to (36) or the zinc oxide-based particlesdescribed in (50) to (58) are used, the cosmetics exhibit IR (inclusiveof near infrared rays (=heat rays) and far infrared ryas)-cutting power.When the zinc oxide-polymer composite particles obtained by the processdescribed in (10) to (18) or the zinc oxide-polymer composite particlesdescribed in (37) to (42) are used, smoothness is imparted to giveexcellent texture. When ultrafine particles are used, the cosmetics haveexcellent visible light transmitting properties (=transparency). whenfine particles having a double layer structure, such as hollowparticles, are used, the cosmetics have light scattering properties andtransparency.

Since the zinc oxide-based particles of the invention mainly compriseZnO, they have excellent antimicrobial properties, thereby providingcosmetics articles having an antimicrobial action.

When fine particles having interstices among crystals and/or a hollowstructure are used, the cosmetics have moisture retaining properties andgive a moisturized feeling. A perfume and the like can be held in suchparticles so as to be released slowly.

The zinc oxide-polymer composite particles obtained by the processdescribed in (10) to (18) and the zinc oxide-polymer composite particlesdescribed in (37) to (42), particularly those having a double layerstructure whose outer shell is made up by agglomeration of theabove-described zinc oxide-based fine particles, exhibit high lightdiffusing properties. Therefore, coated articles obtained by coating atransparent or semitransparent substrate (e.g., glass or plastics) witha coating composition containing such composite particles and resinmolded articles formed of a resin composition containing such compositeparticles are useful as a diffuser applicable to those members whichrequire light diffusion, such as covers of general lights, emergencylights, guiding lights, indicator lights, etc.; display plates orpanels; light transmitting covers; signs or markers and screens forimage projection; and diffusers for back-lighting liquid crystaldisplays (LCD). Of the coating compositions containing such compositeparticles, those for printing ink are especially useful for offsetprinting because the composite particles effectively serve as a mattingagent. Further, diffusers containing the composite particles and therebyshowing improved transparency to visible light and improved visiblelight diffusion are effective for size or thickness reduction of suchequipment as LCD or lights.

The coating composition containing the above-mentioned compositeparticles preferably comprises the composite particles of the invention,a binder component capable of forming a transparent or semitransparentcontinuous phase, and a solvent capable of dispersing and/or dissolvingthe binder component having dispersed therein the composite particles.The amount of the composite fine particles is, for example, 0.1 to 80%by weight, preferably 0.5 to 50% by weight, based on the total solidscontent of the composite fine particles and the binder component.

The coated article obtained by using the above-mentioned compositeparticles comprises a substrate and a coating film formed on the surfaceof the substrate. The substrate is, for example, at least one of a resinmolded article, glass, and paper. The resin molded article is, forexample, at least one of a plate, a sheet, a film, and fiber. Thesubstrate is preferably transparent and/or semitransparent and includessynthetic resins, such as (meth)acrylic resins, polycarbonate resins,polyester resins, polyimide resins, vinyl chloride resins, polystyreneresins, and polyolefin resins; and glass. The coating film comprises thecomposite particles of the invention and the binder component forming atransparent or semitransparent continuous phase in which the compositeparticles are dispersed. The amount of the composite particles is, forexample, 0.1 to 80% by weight, preferably 0.5 to 50% by weight, based onthe total solids content of the composite particles and the bindercomponent.

If the amount of the composite particles exceeds the above range, thecoating film has insufficient adhesion to the substrate and poor scratchresistance or abrasion resistance. If it is lower than that range, theeffects of adding the composite particles are insufficient.

The above-described coating composition contains the composite particlesand the binder component in a total solids content of 1 to 80% by weightand 10 to 99% by weight of a solvent, both based on the total weight ofthe composition. The balance of the composition comprises additivesadded according to necessity, such as pigments.

Where the composite particles have an outer shell made by agglomerationof the zinc oxide-based fine particles, light scattering also takesplace at the interface between the outer shell and the inside, tothereby provide a coating film and a coated article with excellent lightdiffusing properties. Where the polymer also exists in the outer shelland the composite particles are hollow, these characteristics arefurther enhanced.

The resin composition containing the composite particles contains thecomposite particles of the invention and a resin capable of forming atransparent or semitransparent continuous phase. The amount of thecomposite fine particles is, for example, 0.1 to 80% by weight,preferably 0.2 to 20% by weight, based on the total solids content ofthe composite fine particles and the resin.

The resin molded article is an article obtained by molding theabove-described resin composition into a shape selected from the groupconsisting of a plate, a sheet, a film, and fiber. The resin moldedarticle contains the composite particles of the invention and a resinforming a transparent or semitransparent continuous phase in which thecomposite particles are dispersed. The amount of the composite particlesis, for example 0.1 to 80% by weight, preferably 0.1 to 20% by weight,based on the total solids content of the composite particles and theresin.

Where the composite particles have an outer shell made by agglomerationof the zinc oxide-based fine particles, since light scattering alsotakes place at the interface between the outer shell and the inside, theresulting resin molded article has excellent light diffusing properties.Where the polymer also exists in the outer shell and the compositeparticles are hollow, these characteristics are further enhanced.

Accordingly, the coating compositions, coated articles, resincompositions, resin molded articles and cosmetics containing theabove-described composite particles have:

(1) light diffusing properties and light transmitting properties whichowe to the composite particles and are controlled according to the enduse,

(2) UV screening properties,

(3) high dispersibility in cosmetic compositions, and

(4) antimicrobial and antifungal (antibacterial) actions.

The zinc oxide-polymer composite particles obtained by the processdescribed in (10) to (18), the zinc oxide-based fine particles obtainedby the process described in (27) to (36), the zinc oxide-polymercomposite particles described in (37) to (42), and the zinc oxide-basedfine particles described in (50) to (58) can have their light diffusingproperties and light transmitting properties controlled in conformitywith the end use. Therefore, a resin layer containing these compositeparticles or zinc oxide-based particles can be used advantageously as adiffuser for back-lighting liquid crystal displays.

The process for producing the diffuser is not particularly limited. Thediffuser can be produced in accordance with the above-mentionedprocesses for producing a coated article and a resin molded article.

Resins and additives which constitute a diffuser are not limited, andthose used in the above-described resin molded articles can be used.Preferred resins for diffusers are at least one of polyethyleneterephthalate resins, polycarbonate resins, and (meth)acrylic resins.

A diffuser as a coated article can be obtained by applying theabove-described coating composition containing a binder to a transparentsubstrate to form a coating film. A preferred substrate is usually apolyester film or sheet or a polycarbonate film or sheet.

The inorganic compound particles obtained by the process described in(19) to (26) and the inorganic compound particles described in (43) to(49) contain 60 to 100% by weight of zinc oxide and have on theirsurface a cluster of thin plates with their tips projecting outward.Therefore, they are multifunctional fine particles having the followingcharacteristics:

(1) having abnormal light diffusion characteristics,

(2) scattering electromagnetic waves in the near infrared region withoutreducing a percent diffused transmission in the visible light,

(3) being a porous body having an uneven surface and a large surfacearea,

(4) having ultraviolet absorbing and scattering power,

(5) being a light semiconductor, and

(6) having antimicrobial and antifungal actions.

Since the inorganic compound particles function as porous particles ormicrocapsules, they are useful as antimicrobial agents, gas adsorbents,controlled releasing agents and adsorbents as well as theabove-mentioned uses. Structures of these products containing theinorganic compound particles and process for manufacturing them are notparticularly limited, and conventionally known structures and methodsare used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a transmission electron micrograph of powder P14 obtained inExample 14.

FIG. 2 is a transmission electron micrograph of zinc oxide fineparticles in powder P14 obtained in Example 14.

FIG. 3 is a scanning electron micrograph of powder (P32) obtained inExample 32.

FIG. 4 is a scanning electron micrograph of fine particles in powder(P32) obtained in Example 32.

FIG. 5 is a transmission electron micrograph of the cut section of thefine particles in powder (P32) obtained in Example 32.

FIG. 6 is a scanning electron micrograph of fine particles in the powderobtained in Example 33.

FIG. 7 shows spectral transmission curves of the coated article obtainedin Example 39.

FIG. 8 shows spectral transmission curves of the coated article obtainedin Comparative Example 12.

FIG. 9 shows spectral transmission curves of a coated article.

FIG. 10 shows X-ray diffraction patterns of powders.

FIG. 11 shows X-ray diffraction patterns of powders.

FIG. 12 shows spectral transmission curves of a coated article.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be illustrated in greater detail by wayof Examples, but the invention should not be construed as being limitedthereto.

For each dispersion of zinc oxide-based fine particles obtained, variousphysical properties such as the crystalline properties of the fineparticles, the shape of the particles, the primary particle size, thestate of dispersion or agglomeration, the concentration of the fineparticles, the compositions, and the like were analyzed and evaluatedaccording to the following methods. When the dispersion obtained inExamples should be powdered prior to the analysis and evaluation, it waspowdered in accordance with the following method, and the resultingpowder sample was subjected to measurement.

The fine particles obtained in Examples in powder form were subjected toall analyses as they were.

(Preparation of Powder Sample)

The fine particles of a dispersion were separated by centrifugation anddried at 80° C. in vacuo to completely drive out the volatile matter toobtain powder of the fine particles.

(Crystalline Properties)

Evaluated through powder X-ray diffractometry.

(Particle Shape)

Observed through a scanning electron microscope or a transmissionelectron microscope at a magnification of 10,000.

(Particle Size)

The particle diameters of arbitrarily selected 100 particles on ascanning electron micrograph or a transmission electron micrograph of10,000 magnifications were measured to obtain an average particle sizeaccording to the following equation. In the case of using a scanningelectron microscope, a noble metal alloy is deposited on the particlesby vacuum evaporation prior to the measurement. Because the measuredparticle size is increased by the thickness of the deposit as comparedwith that obtained through a transmission electron microscope, themeasured value was corrected accordingly.

Average particle size

d: number average particle size

Di: particle size of individual particles

n: number of particles

(State of Dispersion or Agglomeration)

Evaluated by means of an optical microscope and a centrifugalprecipitation type particle size distribution measuring apparatus andgraded as follows:

A: Primary particles are dispersed.

B: Primary particles are partly agglomerated.

C: Primary particles are agglomerated.

(Concentration of Particles in Dispersion)

An aliquot of a dispersion was vacuum dried at 100° C. until thevolatile matter such as a solvent was completely removed. The weightratio of the resulting powder to the dispersion was taken as aconcentration of the particles in the dispersion.

(Solvent Composition in Dispersion)

The solvent in a dispersion was separated by centrifugation andidentified and determined by mass spectrometry and gas chromatography.

(Composition of Particles)

The composition of particles was determined by total judgement of theanalytical results of a powdered sample obtained through elementaryanalysis, ion chromatography, IR absorption spectrophotometry, NMR,X-ray fluorometry, atomic-absorption spectroscopy, gravimetric analysis,and the like.

(Coefficient of Particle Size Variation)

The particle diameters (major axes) of arbitrary selected 100 particleson a scanning electron micrograph under 10,000 magnifications weremeasured to obtain a number average particle size of fine particles. Thecoefficient of particle size variation was calculated therefromaccording to equation:

 CV=100σ_(n−1) /d _(n)

CV: coefficient of variation of particle size

σ_(n−1): standard deviation of particle size distribution

d_(n): number average particle size

The standard deviation of particle size distribution is calculated fromequation:$\sigma_{n - 1} = {\left( {\sum\limits_{i = 1}^{n}\left( {d_{n} - D_{i}} \right)^{2}} \right)^{1/2}/\left( {n - 1} \right)}$

(Particle Shape)

Judged on the basis of an L/B (major axis/minor axis) ratio obtained bymeasurement on 100 particles on a scanning electron micrograph under10,000 magnifications. The L/B ratio was obtained from equation:${{L/B}\quad {ratio}} = {\left( {\sum\limits_{i = 1}^{n}\left( {L_{i}/B_{i}} \right)} \right)/n}$

L_(i): major axis of individual particles

B_(i): minor axis of individual particles Particles having an L/B ratioof 1.0 or higher and lower than 1.2 were judged to be spherical, andthose having an L/B ratio of 1.2 to 5.0 were judged to be ellipsoidal.

(Size and Shape of Zinc Oxide Fine Particles)

Judged through a scanning electron microscope or a transmission electronmicroscope under 10,000 to 100,000 magnifications.

The micrograph of the cut section of composite fine particles wasobtained by embedding the composite fine particles into a resin, slicingthe preparation to prepare an ultrathin section, which was observedunder a transmission electron micrograph.

(Composition of Fine Particles (Zinc Oxide Concentration))

A powdered sample was calcined in air at 600° C. for 2 hours, and theweight ratio of the resultant ash, taken as zinc oxide, was obtained.

(Optical Characteristics of Fine Particles-Containing Film, etc.)

A transmission at 800 to 200 nm was measured with an autographicspectrophotometer (UV-3100, manufactured by Shimadzu Corporation) toobtain a (total) transmission in the visible region, UV screening power,etc. as spectral characteristics.

The total transmission and a haze were measured with a turbidimeter(NDH-1001 DP, manufactured by Nihon Denshoku Kogyo K.K.).

(Specific Surface Area and Pore Size Distribution of Fine Particles)

Using a powdered sample, a BET specific surface area, a pore sizedistribution, etc. were measured by means of a full-automatic gasadsorption measuring apparatus (AUTOSORB-6, manufactured byYuasa-Ionics).

(Size and Shape of Thin Crystal Grains)

Observed under a scanning electron microscope or a transmission electronmicroscope at a magnification of 10,000 to 100,000.

The micrograph on the section was taken of an ultrathin section ofresin-embedded fine particles under a transmission electron microscope.

(State of Dispersion or Agglomeration)

Evaluated by means of an optical microscope and a centrifugalprecipitation type particle size distribution measuring apparatus andgraded as follows:

A: Fine particles are dispersed without being agglomerated.

B: Fine particles are partly agglomerated.

C: Fine particles are agglomerated.

The weight average particle size d_(w) of the fine particles in adispersion was measured with a centrifugal precipitation type particlesize distribution measuring apparatus.

(Optical Characteristics of Fine Particles (Heat Ray-CuttingPerformance, etc.))

A dispersion of fine particles as obtained by reaction was concentratedto obtain a concentrated dispersion having a particle concentration of10% by weight. The concentrated dispersion was applied to a 2 mm thickglass plate by means of a bar coater with the coating weight beingvaried from 1 to 10 g/m² in terms of the fine particles, and dried at80° C. in a nitrogen atmosphere to form a dry film. The spectralcharacteristics of each dry film were measured at a wavelength of 2200to 200 nm with an autographic spectrophotometer (UV-3100, manufacturedby Shimadzu Corporation). The spectral curve obtained for the filmhaving a coating weight of 3 g/m² in terms of the fine particles wasexamined to evaluate the performances based on the following standards.

Standard Grade UV cutting power: Transmission at 350 nm: ≦1% A 1 to 10%B >10% C Heat ray cutting power: Cut* at 2 μm: >40% +++ 20 to 40% ++<20% + Visible light transmission: Transmission at 600 nm: ≧80% +++ 70to 80% ++ 60 to 70% + <60% − *Cut of heat rays = [transmission (%) ofsubstrate at 2 μm] − [transmission (%) of coated article at 2 μm]

For reference, the transmissions of the glass substrate plate used wereas follows.

wavelength: 350 nm 600 nm  2 μm Transmission (%):  86  91 91

(Optical Characteristics of Coated Article)

Spectral characteristics of coated articles were evaluated by measuringthe transmission at various wavelengths from 2200 to 200 nm with anautographic spectrophotometer (UV-3100, manufactured by ShimadzuCorporation).

Based on the results of measurement, the performances were evaluated asfollows.

Heat ray cut=[transmission (%) of substrate at 2 μm]−[transmission (%)of coated article at 2 μm]

UV cutting power was evaluated in terms of transmission at 350 nm.

A total transmission and a haze value were measured with a turbidimeter(NDH-1001 DP, manufactured by Nihon Denshoku Kogyo K.K.).

(Electrical Conductivity of Fine Particles)

A powdered sample measuring 0.1 ml was sandwiched in between a 1.5cm-square Pyrex glass plate having a comb type electrode formed thereonby vacuum evaporation of gold and a 1.5 cm-square Pyrex glass platehaving no deposit. After the test piece was allowed to stand for 1 hourwith a given pressure applied thereon at a temperature of 20° C. and 60%RH under shielding from light, the electric current (dark current) wasmeasured under the above conditions with Electrometer 617 (manufacturedby Kesley Corp.), which was converted to a surface resistivity (Ω).

The conductivity of the sample was evaluated by comparing the thusobtained resistivity with that of commercially available zinc oxide(Aenka 1-Go Tokusei, produced by Sakai Chemical Industry Co., Ltd.) as areference sample. That is, evaluation was made based on r value(=resistivity of the reference sample/resistivity of the sample underanalysis).

Grade of Range of r Value Conductivity 1 × 10⁻¹ ≦ r < 1 × 10¹ − 1 × 10¹≦ r < 1 × 10² + 1 × 10² ≦ r < 1 × 10³ ++ 1 × 10³ ≦ r +++

EXAMPLE 1

In a 10 l glass-made reactor equipped with a stirrer, a droppingopening, a thermometer, and a reflux condenser, 1.2 kg of acetic acidwas dissolved in a mixed solvent of 2.0 kr of methanol and 2.0 kg ofion-exchanged water, and 1.08 kg of zinc acetate dihydrate was addedthereto. The mixture was heated up to 60° C. while stirring to obtain aunifor zinc-containing solution (A1).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of benzyl alcoholwas charged, and the inner temperature was raised up to 150° C. andmaintained at that temperature. To the heated benzyl alcohol was addeddropwise 6.28 kg of the zinc-containing solution (A1) kept at 60° C.over a period of 30 minutes by means of a constant delivery pump. Thetemperature of the alcohol-based system varied from 150° C. to 138° C.After the dropwise addition, the inner temperature was elevated to 200°C., and the mixture was maintained at that temperature for 5 hours toobtain 5.80 kg of a white dispersion (D1). The dispersion (D1) was adispersion in which crystalline zinc oxide fine particles having aprimary particle size of 40 to 90 nm were dispersed in a considerablysecondarily agglomerated state in a solvent mainly comprising benzylalcohol. As a result of a compositional analysis, the dispersion (D1)was found to have a zinc oxide fine particle concentration of 7.0 wt %and, as a solvent component, a benzyl alcohol content of 61.4 wt % and abenzyl acetate content of 31.6 wt %. The physical properties of thedispersion (D1) and the zinc oxide fine particles in the dispersion (D1)are shown in Table 2 below.

EXAMPLE 2

In the same glass reactor as used in Example 1, 0.3 kg of commerciallyavailable zinc oxide powder was mixed with a mixed solvent of 1.5 kg ofacetic acid and 1.5 kg of ion-exchanged water, followed by heating to80° C. while stirring to prepare a uniform zinc-containing solution(A2).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 150° C. andmaintained at that temperature. To the heated alcohol was added dropwise3.3 kg of the zinc-containing solution (A2) kept at 80° C. over a30-minute period by means of a constant delivery pump. The temperatureof the alcohol-based system varied from 150° C. to 128° C. After thedropwise addition, the inner temperature was increased. When thetemperature reached 160° C., 0.15 kg of a solution of 0.015 kg of lauricacid in 2-butoxyethanol was added thereto and mixed. The temperature wasfurther increased to 170° C., at which the mixture was maintained for 4hours to obtain 9.9 kg of a milky white dispersion (D2).

The dispersion (D2) was substantially a monodispersion in whichcrystalline zinc oxide fine particles having a uniform primary particlesize of 20 nm were dispersed. The physical properties of the dispersion(D2) and the zinc oxide fine particles in the dispersion (D2) are shownin Table 2 below.

EXAMPLE 3

A dispersion of zinc oxide fine particles was prepared in the samemanner as in Example 2, except for altering the reaction conditions,such as the kind or amount of the raw materials and the additive, asshown in Table 1 below. The resulting dispersion was concentrated byevaporating part of the solvent by means of an evaporator under reducedpressure at 120° C. The concentration was adjusted with 2-butoxyethanolto give a dispersion containing 10 wt % of zinc oxide fine particles(D3). The physical properties of the dispersion (D3) and the zinc oxidefine particles in the dispersion are shown in Table 2 below.

EXAMPLE 4

A dispersion of zinc oxide fine particles was prepared in the samemanner as in Example 2, except for altering the reaction conditions,such as the kind or amount of the raw materials and the additives, asshown in Table 1 below. The resulting dispersion was concentrated byevaporating part of the solvent by means of an evaporator at 120° C.under reduced pressure. The concentration was adjusted with2-butoxyethanol to give a dispersion containing 25 wt % of zinc oxidefine particles (D4). The physical properties of the dispersion (D4) andthe zinc oxide fine particles in the dispersion are shown in Table 2below.

EXAMPLE 5

A dispersion of zinc oxide fine particles (D5) was prepared in the samemanner as in Example 2, except for altering the reaction conditions,such as the kind or amount of the raw materials, as shown in Table 1below. The physical properties of the dispersion (D5) and the zinc oxidefine particles in the dispersion are shown in Table 2 below.

TABLE 1 Zinc-Containing Solution Solution Heating Zinc- Carboxyl- Tempe-Alcohol- Temp- Example Containing Containing rature Containing Solutionrature No. Compound Compound Solvent (° C.) Alcohol Additive (° C.) 1zinc acetate acetic acid water 60 benzyl — 200 dihydrate (1.2) (2.0)alcohol (1.08) methanol (12) (2.0) 2 zinc oxide acetic acid water 802-butoxy- lauric 170 (0.3) (1.5) (1.5) ethanol acid (12) (0.015) 3 zincacetic acid water 80 2-butoxy- lauryl- 174 hydroxide (4.0) (1.5) ethanolamine (0.36) (12) (0.033) 4 zinc acetic acid water 80 2-butoxy- Softanol170 hydroxide (4.0) (1.5) ethanol M70 (0.36) (12) (0.067) 5 basic zincacetic acid water 80 2-butoxy- — 174 carbonate*¹ (1.5) (1.5) ethanol(0.020) (12) zinc oxide (0.285) Note: *¹: ZnO content: 74 wt % Thevalues in the parentheses indicate part(s) by weight.

TABLE 2 Physical Properties of Fine Particles Average Composition ofDispersion (wt %) Primary State of Zinc Oxide Example CrystallineParticle Particle Dispersion or Fine Alcoholic Ester No. PropertiesShape Size (nm) Agglomeration Particles Solvent Compound 1 crystalgranular 70 C 7.0 61.4 31.6 2 ″ granular 20 A 3.0 82.0 14.9 3 ″ granular30 B 10.0 41.0 49.0 4 ″ granular 20 B 25.0 40.0 35.0 5 ″ granular 15 A4.2 76.1 19.7

EXAMPLE 6

The dispersion (D2) obtained in Example 2 was concentrated in the samemanner as in Example 3 to obtain a concentrated dispersion (D6) having azinc oxide concentration of 20 wt %. The dispersion (D6) was dilutedwith methanol to obtain a slurry (S6) having a zinc oxide concentrationof 10 wt %. The slurry (S6) was powdered by use of a vacuum flashevaporator.

A long pipe of stainless steel measuring 8 mm in inside diameter and 9 min length was kept heated by passing compressed steam through a jacketcovering the long pipe. The slurry (S6) was continuously supplied fromone end of the long pipe (slurry inlet) at a flow rate of 10 kg/hr by ametering pump. The other end of the long pipe was maintained at areduced pressure of 50 Torr and connected to a bag filter where powderwas separated from the vaporized solvent. The powder (P6) of the zincoxide fine particles thus separated in the bag filter was collected in apowder collecting chamber also kept at 50 Torr.

The resulting powder (P6) was easily dispersible in its primary particlestate in organic solvents, such as aromatic hydrocarbons (e.g.,toluene), ketones (e.g., methyl ethyl ketone), esters (e.g., butylacetate), and alcohols (e.g., methanol and isopropyl alcohol).

COMPARATIVE EXAMPLE 1

A zinc-containing solution (A1) was prepared in the same manner as inExample 1. The solution containing a zinc oxide precursor was addeddropwise to a solvent in the same manner as in Example 1, except forreplacing benzyl alcohol as a solvent by o-xylene. The resulting mixturewas kept at 140° C. for 2 hours to obtain a suspension. X-Raydiffractometry of the suspension revealed that the fine particlescontained were not zinc oxide fine particles.

COMPARATIVE EXAMPLE 2

A zinc-containing solution (A2) was prepared in the same manner as inExample 2. The solution containing a zinc oxide precursor was addeddropwise to a heated solvent in the same manner as in Example 2, exceptfor replacing 2-butoxyethanol as a solvent by ethylene glycol n-butylether acetate. The resulting mixture was kept at 170° C. for 2 hours toobtain a suspension. X-Ray diffractometry of the suspension revealedthat the fine particles contained were not zinc oxide fine particles.

EXAMPLE 8

The dispersion (D2) obtained in Example 2 was concentrated in the samemanner as in Example 3, and the concentration was adjusted with tolueneto give a dispersion (D2-2) containing zinc oxide fine particles in aconcentration of 10 wt %. The dispersion (D2-2) was formulated into acoating composition according to the following formulation:

Formulation of Coating Composition Dispersion (D2-2) 100 parts by weightAlloset 5247 200 parts by weight (produced by Nippon Shokubai KagakuKogyo Co., Ltd.; solid content: 45 wt %) Toluene 100 parts by weight

The coating composition was applied to each of a glass plate, apolyester film and an acrylic resin plate by means of a bar coater anddried to form a coating film. On every substrate, the coating filmscreened out ultraviolet rays effectively while having excellent visiblelight transmitting properties. In Table 3 below are shown the spectraltransmission of the glass plate having the coating film (thickness: 11μm).

COMPARATIVE EXAMPLE 3

A coating composition containing 10 wt % of zinc oxide was prepared inthe same manner as in Example 8, except for using zinc oxide fineparticles obtained by a French process (average primary particle size:0.04 μm) in place of the dispersion (D2) as used in Example 8, andapplied to a glass plate in the same manner to form a coating layerhaving a thickness of 10 μm. The coating film had lower transparency anda lower UV cutting ratio than the coating film obtained in Example 8.The spectral transmission of the glass plate having the coating film areshown in Table 3.

TABLE 3 Visible Light UV Transmission Transmission (500 nm) (360 nm)Coated glass plate obtained 80 2 in Example 8 Coated glass plateobtained 73 10 in Comparative Example 3 Glass plate 90 86

EXAMPLE 9

A dispersion (D2-2) was obtained in the same manner as in Example 8 andwas formulated into a coating composition according to the followingformulation:

Formulation of Coating Composition

Dispersion (D2-2) 100 parts by weight

Silica sol 120 parts by weight

(OSCAL 1432, produced by Shokubai Kasei Kogyo Co., Ltd.)

Isopropyl alcohol 100 parts by weight

The coating composition was applied to a glass plate by means of a barcoater and dried to form a coating film. The coating film was ascratch-resistant film having excellent visible light transmittingproperties and yet UV absorbing properties.

EXAMPLE 10

Ten parts by weight of the powder (P6) obtained in Example 6 and 500parts by weight of polycarbonate resin pellets were mixed andmelt-kneaded to obtain a molten mixture having uniformly dispersedtherein 2 wt % of zinc oxide fine particles. Subsequently the mixturewas extruded into a polycarbonate plate (A) having a thickness of 2 mm.The polycarbonate plate (A) effectively cut ultraviolet rays whilehaving excellent visible light transmitting properties.

EXAMPLE 11

The dispersion (D2) obtained in Example 2 was subjected tocentrifugation to remove the solvent. The resultant zinc oxide fineparticles containing a slight amount of a residual solvent componentwere dispersed in methyl methacrylate (hereinafter abbreviated as MMA),and the dispersion was again centrifuged. The above operation wasrepeated several times to finally obtain 50 parts by weight of an MMAdispersion containing 20 wt % of the zinc oxide fine particles.

To 50 parts by weight of the MMA dispersion was added 0.4 part by weightof a polymerization initiator V-65, and the dispersion was added to 200parts by weight of a 5 wt % aqueous solution of Poval (PVA 205, producedby Kuraray Co., Ltd.), followed by stirring for 5 minutes. The mixturewas further dispersed in a disperser to prepare a suspension containingthe zinc oxide fine particles in MMA as a dispersing medium.

The suspension was put in a glass container equipped with a stirrer, areflux condenser and a thermometer and kept at 70° C. for 30 minuteswith stirring. The temperature was gradually raised, and the system wasmaintained at 95° C. or higher for 3 hours to cause MMA to polymerize toobtain an aqueous suspension of particles of polymethyl methacrylate(hereinafter abbreviated as PMMA) containing the zinc oxide fineparticles. The suspension was centrifuged, and the solid was washed withwater. After repeating the centrifugation and washing several times, theparticles were dried at 60° C. to obtain PMMA particles containing thezinc oxide fine particles. As a result of analysis, the PMMA particleswere found to be composite particles having a particle size of 10 to 70μm and a zinc oxide content of 18 wt % in which the zinc oxide fineparticles were uniformly dispersed in PMMA. The PMMA particleseffectively cut ultraviolet rays and are useful as, for example, afiller for cosmetics.

EXAMPLE 12

Ten parts by weight of the powder (P6) obtained in Example 6 and 100parts by weight of polyester resin pellets were mixed and melt-kneadedto obtain a polyester composition having uniformly dispersed therein 5wt % of zinc oxide fine particles. The composition was extruded into asheet, and the extruded sheet was stretched to obtain a polyester filmhaving a thickness of 50 pm. The film was a substantially transparentfilm in which the zinc oxide fine particles were uniformly and highlydispersed and which cut ultraviolet rays effectively.

In the same manner, a polyester composition containing 5 wt % of thezinc oxide fine particles was prepared and melt-spun to obtain polyesterfiber. The resulting fiber had uniformly and highly dispersed thereinthe zinc oxide fine particles and cut ultraviolet rays effectively.

EXAMPLE 13

The dispersion (D5) obtained in Example 5 was subjected tocentrifugation to remove the solvent. The resultant zinc oxide fineparticles containing a slight amount of a residual solvent componentwere dispersed in ion-exchanged water, followed by centrifugation again.The above operation was repeated several times, and the finally obtainedzinc oxide fine particles were dispersed in ion-exchanged water to give50 parts by weight of an aqueous dispersion (D5-2) containing 20 wt % ofthe zinc oxide fine particles.

The aqueous dispersion (D5-2) was mixed with an acrylic resin emulsion(Acryset® ES-285E, produced by Nippon Shokubai Co., Ltd.) as a binderresin to prepare a coating composition. Polyester fiber was soaked inthe coating composition and dried to obtain polyester fiber having thezinc oxide fine particles at an add-on of 0.5 g/m². The resulting fiberexhibited improved light resistance.

EXAMPLE 14

In a glass reactor equipped with a stirrer, a dropping opening, athermometer, and a reflux condenser, 0.3 kg of commercially availablezinc oxide powder was mixed with a mixed solvent of 1.5 kg of aceticacid and 1.5 kg of ion-exchanged water, followed by heating to 80° C.while stirring to dissolve the zinc oxide in the mixed solvent to obtaina uniform zinc-containing solution.

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 154° C. andmaintained at that temperature. To the heated alcohol was added dropwise3.3 kg of the zinc-containing solution kept at 80° C. over a 30-minuteperiod by means of a constant delivery pump. With the dropwise addition,the temperature of the alcohol-based system decreased from 154° C. to134° C. After the dropwise addition, the inner temperature wasincreased. When the temperature reached 167° C., 1.5 kg of a solution of53 g of a methyl methacrylate-acrylic acid copolymer (methylmethacrylate/acrylic acid=9/1 by weight; weight average molecularweight: 7,500) in 2-butoxyethanol was added thereto and mixed. Thetemperature was further increased to 170° C., at which the mixture wasmaintained for 2 hours to obtain 10.65 kg of a dispersion of fineparticles.

The fine particles were removed from the dispersing medium bycentrifugation, washed with isopropyl alcohol, and dried in vacuo (10Torr) at 50° C. for 24 hours to obtain powder P14 of the fine particles.

The powder P14 had a number average particle size of 2.0μ as measuredfrom its scanning electron micrograph. Observation under a transmissionelectron microscope revealed that the powder P14 had a double layerstructure in which zinc oxide fine particles having a particle size of 8to 30 nm (number average particle size: 20 nm) were localized in theouter shell. The powder P14 was broken, and the broken particles wereobserved under a scanning electron microscope to find the fine particleshollow. The ZnO content in the powder P14 was found to be 87.7 wt %. Thezinc oxide fine particles were confirmed to be ZnO crystals throughX-ray diffractometry. The elementary analysis, FT-IR, etc. providedconfirmation that the powder P14 contained the methylmethacrylate-acrylic acid copolymer. It was confirmed from all theseresults that the powder P14 was zinc oxide-polymer composite fineparticles.

The cross section of the fine particles obtained with a transmissionelectron microscope is shown in FIG. 1, and the transmission electronmicrograph of the ZnO ultrafine particles present in the outer shell isshown in FIG. 2. The small black dots in FIG. 1 indicate zinc oxide fineparticles. It is seen that a great number of the small black dots gatherto form the outer shell of the lumpy composite fine particles. In FIG.2, the line at the bottom right-hand corner of the picture is 20 nm longfrom end to end. In FIG. 2, the images of gray to black are zinc oxidefine particles. It is seen that a number of the zinc oxide fineparticles are agglomerated.

The powder P14 was evaluated for gas adsorbing properties (deodorizingperformance). The powder P14 weighing 1 g was put in a Tedlar bag, 3 lof air was introduced therein, and the bag was sealed. Then,trimethylamine was put in the bag, and the bag was allowed to stand atroom temperature. The change in trimethylamine concentration in the bagwas measured with time. The same test was carried out on methylmercaptanand propionic acid. The results obtained are shown below (gasconcentration after a prescribed time period was relatively expressedtaking the initial gas concentration as 100).

10 min 1 hr 3 hrs Trimethylamine 57 45 39 Methylmercaptan 52 25 18Propionic acid 100 59 14

EXAMPLES 15 TO 18

Dispersions of zinc oxide-polymer composite fine particles were preparedin the same manner as in Example 14, except for replacing the methylmethacrylate-acrylic acid copolymer with the polymer shown in Table 4below and altering the reaction conditions as shown in Table 4. PowdersP15 to P18 of the composite fine particles were obtained from theresulting dispersions in the same manner as in Example 14. The physicalproperties of the polymers P14 to P5 are shown in Table 5 below.

TABLE 4 Reaction Conditions Zn-Monocarboxylic Acid Solution PolymerSolution Added Mono- Amount carbox- Solu- Reaction Exam- of ReactionZinc ylic tion Time & ple Polymer Solvent Source Acid Solvent Temp.Tempe- No. Polymer (kg) Solvent (kg) (kg) (kg) (kg) (° C.) rature*¹ 14methyl methacrylate- 53 2-butoxy 2- zinc acetic water 80 170° C. acrylicacid copolymer ethanol butoxy oxide acid (1.5) 3 hrs (MW: 7,500; ethanol(0.3) (1.5) COOH equiv.: 770) (12) 15 acrylic acid-hydroxy- 92 2-butoxy2- zinc acetic water 60 170° C. ethyl methacrylate- ethanol butoxy oxideacid (1.5) + 3 hrs styrene lauryl meth- ethanol (0.3) (1.5) methanolacrylate copolymer (Mw: (12) (1.5) 20,000; COOH equiv.: 3000) 16 methylmethacrylate- 40 2-butoxy benzyl zinc propionic water 40 200° C.methacrylamide copolymer ethanol alcohol oxide. acid (1.5) + 0.5 hr (Mw:5,000; amide equiv.: (5.5) + 2H₂O (0.4) + methanol 500) tri- (0.81)acetic (3.0) ethylene acid glycol (1.0) (4.5) 17 polymethyl methacrylate20 propylene 2-butoxy zinc acetic water 80 165° C. (Mw: 120,000) glycolethanol oxide. acid (1.5) 1 hr methyl (12) 2H₂O (1.5) ether (0.81)acetate 18 methyl methacrylate- 120  cyclo- cyclo- zinc iso- water 80140° C. methacryloxypropyltri- hexanol hexanol oxide butyric (1.5) 1 hrmethoxysilane copolymer (10) + (0.3) acid (Mw: 105,000) diethylene(0.2) + glycol (3) + acetic dimethyl- acid formamide (1.0) (2) Note:*The time and temperature for/at which the system was maintainedfinally.

TABLE 5 Zinc Oxide-Polymer Composite Fine Particles Number Coeffi-Average cient of Zinc Number Average Particle Size Oxide Particle SizeExample Powder Size Variation Inside Content of ZnO Particles No. SampleShape (μm) (%) Structure (wet %) (nm) 14 P14 spherical 2.0 18 doublelayer structure 87.8 20 (ZnO localized in outer shell) 15 P15 spherical1.4  4 double layer structure 76.5 15 (ZnO localized in outer shell) 16P16 spherical 5.1  8 double layer structure 85.7 150  (ZnO localized inouter shell) 17 P17 nearly 2.0 22 homogeneous structure 93.0 80spherical (ZnO dispersed (ellipsoidal) uniformly) 18 P18 spherical 0.4514 double layer structure 69.2 10 (ZnO localized in outer shell)

EXAMPLES 19 TO 21

Coating compositions (1) to (3) having the following formulation wereprepared by using the powder P14 obtained in Example 14.

Coating Coating Coating Composition Composition Composition (1) (2) (3)(Example 19) (Example 20) (Example 21) Formulation (part by weight):Powder P14 10 20 30 Acrylic resin polymer 200 178 156 solution* Toluene250 222 194 *: Alloset 5247, produced by Nippon Shokubai Co., Ltd.;solid content: 45 wt %.

Each of the coating compositions (1) to (3) was applied to a glass plateand dried to obtain coated articles (1) to (3) having formed thereon acoating film whose thickness is shown below. The optical properties ofthe coated articles (1) to (3) are also shown below.

Film Total Coated Thickness Transmission Haze Article (μm) (%) (%)Example 19 (1) 21 87 74 Example 20 (2) 19 78 86 Example 21 (3) 18 70 90Glass plate — none 91 0.3

As is shown above, the coated articles of the invention have a greatlyincreased haze, which is indicative of light diffusion properties, overthat of the glass plate substrate, while the total transmission of thecoated articles is almost equal to or at least about 75% of that of theglass plate.

COMPARATIVE EXAMPLES 4 AND 5

Comparative coating compositions (1) and (2) were prepared in the samemanner as in Example 19, except for replacing the powder P14 withultrafine particles of ZnO having an average particle size of 0.02 μm(Comparative Example 4) or zinc oxide fine particles obtained by aFrench process (Aenka 1-Go Tokusei, a product of Sakai Chemical IndustryCo., Ltd.). The coating compositions (1) and (2) were each applied to aglass plate and dried to obtain comparative coated articles (1) and (2),respectively, in the same manner as in Example 19. The opticalproperties of the comparative coated articles (1) and (2) are shown inthe following table.

Comparative Film Total Coated Thickness Transmission Haze Article (μm)(%) (%) Comparative (1) 25 89 60 Example 4 Comparative (2) 25 71 78Example 5

Comparing Examples 19 to 21 with Comparative Examples 4 to 5, it isapparent that the compositions containing the specific composite fineparticles of the invention exhibit excellent light diffusion (diffusetransmission=total transmission×haze) while having a high percenttransmission (total transmission) and that such excellent lightdiffusion properties are manifested even through the amount of thecomposite fine particles in the composition is small.

EXAMPLES 22 AND 23

A coating composition (4) was prepared by using the powder P14 obtainedin Example 14 according to the following formulation.

Formulation of Coating Composition (4): Powder P14  10 parts by weightAcrylic resin polymer solution 200 parts by weight (Alloset 5247,produced by Nippon Shokubai Co., Ltd.; solid content: 45 wt %) Toluene250 parts by weight

The coating composition was applied to a polyester film or a methacrylicresin plate and dried to obtain a coated article (4) or (5),respectively. The optical properties of the resulting coated articlesare shown in the following table.

Film Total Thick- Trans- UV- Coated ness mission Haze Screening Article(μm) (%) (%) Power Example 22 (4) 5 88 20 exhibited Example 23 (5) 33 8677 exhibited

EXAMPLE 24

Two parts by weight of the powder P17 obtained in Example 17 and 998parts by weight of polycarbonate resin pellets were mixed andmelt-kneaded to obtain a molten composition having uniformly dispersedtherein 0.2 wt % of the fine particles. The composition was extrudedinto a plate having a thickness of 5.0 mm. The resulting polycarbonateplate had highly dispersed therein the composite fine particles andexhibited excellent visible light transmission, having a totaltransmission of 85% or more, and excellent ultraviolet screeningeffects.

EXAMPLE 25

Twenty-five parts by weight of the powder P14 obtained in Example 14 and475 parts by weight of methacrylic resin pellets were mixed andmelt-kneaded to obtain a molten composition having uniformly dispersedtherein 5 wt % of the fine particles. The composition was extruded intoa sheet having a thickness of 2 mm. The resulting methacrylic resinsheet had highly dispersed therein the fine particles and exhibited highvisible light transmitting properties and excellent light diffusingproperties, having a total transmission of 83% and a haze of 86%, andexcellent ultraviolet screening effects.

COMPARATIVE EXAMPLE 6

A 2 mm thick methacrylic resin sheet containing 5 wt % of fine particleswas obtained in the same manner as in Example 25, except for replacingthe powder P14 with 25 parts by weight of zinc oxide fine particlesobtained by a French process (Aenka 1-Go, a product of Sakai ChemicalIndustry Co., Ltd.). The resulting sheet contained the fine particles ina secondarily agglomerated and non-uniform state and was white turbid,lacking transparency.

EXAMPLE 26

Two parts by weight of the powder P15 obtained in Example 15 and 98parts by weight of polyester resin pellets were mixed and melt-kneadedto obtain a polyester composition having uniformly dispersed therein 2wt % of the composite fine particles. The composition was extruded intoa sheet, and the extruded sheet was stretched to obtain a polyester filmhaving a thickness of 40 μm. The film had uniformly and highly dispersedtherein the fine particles and was excellent in visible lighttransmission, light diffusion, and ultraviolet screening.

COMPARATIVE EXAMPLE 7

A 40 μm thick polyester film containing 2 wt % of zinc oxide fineparticles was obtained in the same manner as in Example 26, except forreplacing the powder P15 obtained in Example 15 with zinc oxide fineparticles obtained by a French process (Aenka 1-Go, a product of SakaiChemical Industry Co., Ltd.). The resulting film contained the fineparticles in a secondarily agglomerated state and therefore had a poorUV screening effect and was white turbid, lacking transparency.

The surface of the films obtained in Example 26 and Comparative Example7 was observed under a transmission electron microscope. As a result,the surface of the film of Example 26 was found covered with uniform andfine projections because of the existence of fine particles, whereas thesurface of the film of Comparative Example 7 was found to have poorquality due to non-uniform projections, including coarse projectionsresulting from agglomeration of fine particles.

EXAMPLE 27

A polyester composition containing 2 wt % of powder P17 was prepared inthe same manner as in Example 26 except for replacing the powder 15 asused in Example 26 with powder P17 obtained in Example 17. The resultingpolyester composition was melt-spun to obtain polyester fiber. The fiberhad uniformly and highly dispersed therein the fine particles andexhibited transparency and an excellent UV screening effect.

COMPARATIVE EXAMPLE 8

Polyester fiber containing zinc oxide fine particles was obtained in thesame manner as in Example 27 except for replacing the powder P17 withzinc oxide fine particles obtained by a French process (Aenka 1-Go, aproduct of Sakai Chemical Industry Co., Ltd.). The resulting fibercontained the fine particles in a secondarily agglomerated state andtherefore had a low UV screening effect and was white turbid, lackingtransparency.

EXAMPLE 28

The dispersion obtained in Example 17 was subjected to centrifugation toremove the solvent. The resultant composite fine particles containing aslight amount of the residual solvent component were dispersed inion-exchanged water, followed by centrifugation again. The aboveoperation was repeated several times, and the finally obtained particleswere dispersed in ion-exchanged water to give 50 parts by weight of anaqueous dispersion containing 20 wt % of the fine particles.

Fifty parts by weight of the aqueous dispersion were mixed with 20 partsby weight of an acrylic resin emulsion (Acryset® ES-285E, produced byNippon Shokubai Co., Ltd.; solids content: 50 wt %) as a binder toprepare a coating composition. Polyester fiber was soaked in the coatingcomposition and dried to obtain polyester fiber having the fineparticles at an add-on of 7.0 g/m². The resulting fiber exhibitedexcellent transparency and effectively cut ultraviolet light.

COMPARATIVE EXAMPLE 9

Ten parts by weight of zinc oxide fine particles obtained by a Frenchprocess (Aenka 1-Go, a product of Sakai Chemical Industry Co., Ltd.)were mixed with 40 parts by weight of ion-exchanged water and dispersedby means of an ultrasonic homogenizer to give 50 parts by weight of anaqueous dispersion containing 20 wt % of the fine particles. Polyesterfiber having an add-on of 6.8 g/m² of the fine particles was obtained byusing the resulting aqueous dispersion in the same manner as in Example28. The resulting fiber exhibited a UV-screening effect but was whiteturbid.

EXAMPLE 29

A cosmetic (O/W type cream) containing the powder P17 obtained inExample 17 was prepared according to the following formulation.

Formulation:

Aqueous Phase:

(a) Powder  6 parts by weight (b) Propylene glycol  5 parts by weight(c) Glycerin 10 parts by weight (d) Potassium hydroxide  0.2 part byweight (e) Ion-exchanged water 45 parts by weight

Oily Phase:

(f) Cetanol 5 parts by weight (g) Liquid paraffin 5 parts by weight (h)Stearic acid 3 parts by weight (i) Isostearyl myristate 2 parts byweight (j) Glycerol monostearate 2 parts by weight

The components (a) to (e) were mixed by stirring to prepare an aqueousphase, which was kept at 80° C. The components (f) to (j) were mixeduniformly to prepare an oily phase, which was kept at 80° C. The oilyphase was added to the aqueous phase, followed by stirring. The mixturewas emulsified by means of a homomixer, followed by cooling to roomtemperature to obtain cream. The resulting cream was clear and yet had aUV screening effect.

EXAMPLE 30

Cream was prepared in the same manner as in Example 29, except forreplacing the powder P17 with the powder P14 obtained in Example 14.

The resulting cream had an excellent UV screening effect.

COMPARATIVE EXAMPLE 10

Cream was prepared in the same manner as in Example 29, except forreplacing the powder P17 obtained in Example 17 with zinc oxide fineparticles obtained by a French process (Aenka 1-Go, a product of SakaiChemical Industry Co., Ltd.).

In the resulting cream the fine particles were dispersed poorly.Therefore, the cream had a rough feel and poor spreadability. Besides,it was nontransparent due to high whiteness.

EXAMPLE 31

The powder P15 obtained in Example 15 was mixed with ion-exchanged waterto prepare an aqueous dispersion containing 10 wt % of the fineparticles.

Separately, filter paper for quantitative determination (No. 5C, aproduct of Toyo Roshi K.K.) was beaten in a Niagara type beater intopulp having a C.S. freeness of 400 cc. The above prepared aqueousdispersion was added to the pulp to give a fine particle to pulp weightratio of 1 wt %. The resulting pulp slurry was diluted to a solidscontent of 0.1 wt %, dehydrated in a TAPPI sheeting machine, and pressedto obtain a web having a basis weight of 75 g/m², which was then driedin a rotary drier at 100° C. to obtain paper containing 1 wt % of thefine particles. The resulting paper showed a satisfactory particledispersed state and therefore exhibited excellent UV screeningproperties and had high surface flatness.

COMPARATIVE EXAMPLE 11

Paper was prepared in the same manner as in Example 31, except forreplacing the powder P15 obtained in Example 15 with zinc oxide fineparticles obtained by a French process (Aenka 1-Go, a product of SakaiChemical Industry Co., Ltd.). The resulting paper contained the fineparticles in secondarily agglomerated state and therefore had a poor UVscreening effect. Further, the paper had poor surface conditions withcoarse projections due to the agglomerated particles.

EXAMPLE 32

In a glass-made reactor equipped with a stirrer, a dropping opening, athermometer, and a reflux condenser, 0.3 kg of commercially availablezinc oxide powder was mixed with a mixed solvent of 1.5 kg of aceticacid and 1.5 kg of ion-exchanged water. The mixture was heated up to 80°C. while stirring to prepare a uniform zinc-containing solution (A32)comprising zinc oxide dissolved in the mixed solvent.

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 154° C. andmaintained at that temperature. To the heated alcohol was added dropwise3.3 kg of the zinc-containing solution (A32) kept at 80° C. over a30-minute period by means of a constant delivery pump. The temperatureof the alcohol-based system varied from 154° C. to 134° C. After thedropwise addition, the inner temperature was increased. When thetemperature reached 167° C., 0.15 kg of a solution of 6.6 g of lacticacid in 2-butoxyethanol was added thereto and mixed. The temperature wasfurther increased to 170° C., at which the mixture was maintained for 2hours to obtain 10.0 kg of a dispersion (D32).

The fine particles contained in the dispersion (D32) had a weightaverage particle size of 2.0 μm as measured with a centrifugalprecipitation type particle size distribution measuring apparatus.

The fine particles of the dispersion (D32) were separated from thedispersion medium by centrifugation, washed with methanol, and dried invacuo (10 Torr) at 80° C. for 12 hours to obtain powder of the fineparticles (P32).

The powder (P32) was made up of spherical fine particles having a numberaverage particle size of 2.0 μm as measured from its scanning electronmicrograph, with a coefficient of particle size variation of 3.4% and anL/B ratio of 1.06.

On performing calculation based on the weights of the dispersion (D32)and the powder (P32), the dispersion (D32) was found to be the one inwhich the individual particles of the powder (P32) were dispersed in aconcentration of 3.1 wt % without undergoing secondary agglomeration.

The microstructure of the fine particles in the dispersion (D32) wasanalyzed under a scanning electron microscope and a transmissionelectron microscope. It was confirmed that the fine particles wereclusters of thin plate crystals stacked one on another, each thin flatplate having an average thickness of 70 nm and an average major axis of250 nm. It was also confirmed that the thin flat plates were zinc oxidecrystals as a result of powder X-ray diffractometry of the fineparticles and that the fine particles contained 96.0 wt % of zinc oxide(ZnO).

The scanning electron micrograph of the fine particles in the powder(P32) and the transmission electron micrograph of the cut section of thefine particles are shown in Figures. FIG. 3 is a scanning electronmicrograph of the powder (P32), in which the white to gray beads arefine particles of the powder (P32). FIG. 4 is a scanning electronmicrograph of the individual fine particles in the powder (P32), inwhich the eleven white spots at the lower part of the picture were 860nm long from end to end. In FIG. 4, the individual fine particles haveon their surface a cluster of thin plates each having a rounded, long,and narrow shape. The cluster comprises thin plate like zinc oxidecrystals. FIG. 5 is a transmission electron micrograph of the cutsection of the individual fine particles in the powder (P32), in whichthe line at the bottom right-hand corner of the picture is 500 nm longfrom end to end. In FIG. 5, each fine particle has on its surface acluster of thin plates with their end facing outward (the black sharpprojections). The cluster have interstices among the individual thinplates. The individual fine particles are hollow, having almost nocrystals in their inside.

It was confirmed that the individual fine particles were porous fineparticles having a specific surface area of 16.9 m²/g and a pore size of4 nm.

The dispersion (D32) was heated at 120° C. under reduced pressure in anevaporator to evaporate part of the solvent. The thus concentrateddispersion was diluted with isopropyl alcohol to prepare a dispersion(D32a) containing 40 wt % of the fine particles.

The powder (P32) was evaluated for gas adsorbing properties (deodorizingperformance). The powder (P32) weighing 1 g was put in a Tedlar bag, 3 lof air was introduced therein, and the bag was sealed. Then,trimethylamine was put in the bag, and the bag was allowed to stand atroom temperature. The change in trimethylamine concentration in the bagwas measured with time. The same test was carried out on methylmercaptanand propionic acid. The results obtained are shown below (gasconcentration after a prescribed time period was relatively expressedtaking the initial gas concentration as 100).

10 min 1 hr 3 hrs Trimethylamine 77 77 73 Methylmercaptan 85 38 25Propionic acid 88 21 8

The antimicrobial activity of the powder (P32) was evaluated. Asuspension of microbial cells of E. coli and Staph. aureaus wasinoculated to an agar plate medium containing the powder (P32) in avaried concentration and cultivated. The minimum concentration of thepowder (in the agar medium) at which the growth of the bacteria wereinhibited, i.e., minimum inhibition concentration (MIC), was obtained.The results are shown below.

E. coli Staph. aureaus MIC (μg/ml) 3200 1600

The antimicrobial activity of zinc oxide powder prepared by a Frenchprocess (Aenka 1-Go, a product of Sakai Chemical Industry Co., Ltd.; BETspecific surface area: 2.9 m²/g; average particle size: 0.52 μm) wasexamined in the same manner as described above. As a result, the MICagainst E. coli was as high as 100000 μg/ml or more.

EXAMPLE 33

A dispersion of fine particles (D33) was obtained in the same manner asin Example 32, except for changing the amount of lactic acid added asshown in Table 6. The state of dispersion or agglomeration of the fineparticles in the resulting dispersion and various physical properties ofthe dispersed fine particles are shown in Table 6.

The scanning electron micrograph of the fine particles in the powderobtained in Example 33 is shown in FIG. 6. The big and bright ellipse inthe center of FIG. 6 is a single fine particle. In FIG. 6, the fineparticle has on its surface a cluster of thin and rounded plates havinga long and narrow shape or a fan shape. The cluster is made up of thinplates that are thin plate like zinc oxide crystals.

EXAMPLE 34

A dispersion of fine particles (D34) was prepared in the same manner asin Example 32, except for replacing zinc oxide as a zinc source withzinc acetate, using propionic acid in combination as a monocarboxylicacid, and changing the amount of lactic acid added as shown in Table 6.The state of dispersion or agglomeration of the fine particles in thedispersion (D34) and the physical properties of the fine particles areshown in Table 7.

EXAMPLE 35

In a glass-made reactor equipped with a stirrer, a dropping opening, athermometer, and a reflux condenser, 0.3 kg of commercially availablezinc oxide powder and 11.1 g of zinc lactate trihydrate were mixed witha mixed solvent of 1.5 kg of acetic acid and 1.5 kg of ion-exchangedwater. The mixture was heated up to 80° C. while stirring to prepare auniform zinc-containing solution (A35) comprising zinc oxide and zinclactate dissolved in the mixed solvent.

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 160° C. andmaintained at that temperature. To the heated alcohol was added dropwisethe whole amount of the zinc-containing solution (A35) kept at 80° C.over a 30-minute period by means of a constant delivery pump. Thetemperature of the alcohol-based system dropped from 160° C. to 140° C.After the dropwise addition, the inner temperature was increased. Whenthe temperature reached 170° C., the mixture was maintained at thattemperature for 2 hours to obtain 9.1 kg of a dispersion (D35).

The state of dispersion or agglomeration of the fine particles in thedispersion (D35) and the physical properties of the fine particles areshown in Table 7.

EXAMPLE 36

A dispersion of fine particles (D36) was prepared in the same manner asin Example 35, except for changing the amounts of the raw materials usedfor the preparation of the zinc-containing solution as shown in Table 6.The state of dispersion or agglomeration of the fine particles in thedispersion (D36) and the physical properties of the fine particles areshown in Table 7.

EXAMPLE 37

A dispersion of fine particles (D37) was prepared in the same manner asin Example 35, except for changing the amounts of the raw materials usedfor the preparation of the zinc-containing solution as shown in Table 6.The state of dispersion or agglomeration of the fine particles in thedispersion (D37) and the physical properties of the fine particles areshown in Table 7.

The reaction conditions used in Examples 32 to 37 are shown in Table 6,and the physical properties of the fine particles obtained in Examples32 to 37 are shown in Table 7.

TABLE 6 Reaction Conditions Monocarboxylic Zinc Source Acid Lactic AcidSource Reaction Example Amount Amount Amount Molar Ratio Stage of Temp.& No. Kind (kg) Kind (kg) Kind (g) to Zinc Addition Time* 32 zinc 0.3acetic 1.5 lactic 6.6 2 at the 170° C. oxide acid acid heating 2 hrs 33zinc 0.3 acetic 1.5 lactic 1.7 0.5 at the 170° C. oxide acid acidheating 0.5 hr 34 zinc 0.81 propionic 0.4 lactic 16.6 5 at the 170° C.acetate acid acid heating 5 hrs dihydrate acetic 1.0 acid 35 zinc 0.3acetic 1.5 zinc 11.1 2 at the 170° C., oxide acid lactate prepn. of 1 hrtrihydrate Zn-con- taining solution 36 zinc 1.00 isobutyric 0.2 zinc81.2 12 at the 170° C. acetate acid lactate prepn. of 10 hrs dihydrateacetic 1.0 trihydrate Zn-con- acid taining solution 37 zinc 0.37 acetic1.5 calcium 12.2 3 at the 170° C. hydroxide acid lactate prepn. of 1 hrZn-con- taining solution Note: *The time and temperature for/at whichthe system was maintained finally.

TABLE 7 Characteristics of Fine Particles Number Coeffi- Cluster ofAverage cient Thin plates State of Inorganic Compound Part- of SizeMajor Example Dispersion or Amount cle Size Variation L/B Flat- Axis No.Agglomeration Kind (wt %) Shape (μm) (%) Ratio ness (μm) 32 A zinc oxide96.0 spherical 2.0 3.4 1.06 13 0.40 33 A zinc oxide 97.9 nearly 5.5 5.71.90 17 0.33 spherical 34 B zinc oxide 92.8 spherical 1.4 9.3 1.08 6.70.15 35 A zinc oxide 94.4 spherical 2.0 4.5 1.30 10 0.62 (spindle-shape) 36 C zinc oxide 80.1 spherical 2.4 18.0 1.04 105 0.84 37 B zincoxide 93.5 spherical 2.2 12.0 1.07 7.0 0.20

EXAMPLE 38

Methanol was added to the dispersion (D32a) obtained in Example 32 toprepare a slurry (S38) having a zinc oxide concentration of 10 wt %. Theslurry (S38) was powdered in a vacuum flash evaporator illustratedbelow.

The vacuum flash evaporator had a jacketed stainless steel long pipe of8 mm in inner diameter and 9 m in length. The long pipe was heated to200° C. by circulating pressurized steam through the jacket. The slurry(S38) was continuously fed from one end of the long pipe (feed opening)at a flow rate of 10 kg/hr by a constant delivery pump. The other end ofthe long pipe was maintained at a reduced pressure of 50 Torr andconnected to a back filter where powder is separated from the evaporatedsolvent. The powder (P38) of the zinc oxide fine particles thusseparated was collected in a powder collecting chamber also kept at 50Torr.

The resulting powder (P38) was easily dispersible in organic solvents,such as aromatic hydrocarbons (e.g., toluene), ketones (e.g., methylethyl ketone), esters (e.g., butyl acetate), and alcohols (e.g.,methanol and isopropyl alcohol).

The resulting powder (P38) was substantially equal to the fine particlesas dispersed in the dispersion (D32) in terms of particle size andshape, size and shape of the zinc oxide crystals, and the like.

EXAMPLE 39

A coating composition was prepared by using the dispersion (D32a)obtained in Example 32 according to the following formulation.

Formulation of Coating Composition:

Dispersion (D32a) 100 parts by weight Toluene 250 parts by weightAlloset 5247 (aqueous acrylic  4.5 parts by weight resin emulsionproduced by Nippon Shokubai Co., Ltd.; solid content: 45 wt %)

The coating composition was applied to each of a glass plate, apolyester film, and an acrylic resin plate and dried to form a coatingfilm having a thickness of about 2 μm. The coating film on everysubstrate had a high diffuse transmission in the visible region andexhibited a heat ray screening effect as well as an excellent UVscreening effect. Moreover, it assumed a pale pink or green colordepending on the viewing angle or angle of light incidence, producing anextremely attractive appearance. The spectral transmission curves (adiffuse transmission curve and a vertical transmission curve) of thecoated glass plate are shown in FIG. 7, in which T₁ is a diffusetransmission curve, T₂ a vertical transmission curve, and T3 a diffusiontransmission curve of the uncoated glass plate.

COMPARATIVE EXAMPLE 12

A coating composition having a zinc oxide concentration of 10 wt % wasprepared in the same manner as in Example 39, except for replacing thedispersion (D32a) with a dispersion of zinc oxide fine particlesobtained by a French process (Aenka 1-Go, a product of Sakai ChemicalIndustry Co., Ltd.) in isopropyl alcohol, and the composition wasapplied to a glass plate to form a coating film having a thickness of 10μm. The coating film was a white film having no characteristic in color.The spectral transmission curves (diffuse transmission curve T₁ andvertical transmission curve T₂) of the coated glass are shown in FIG. 8.

The comparison between FIGS. 7 and 8 proves that the coating filmcontaining the fine particles obtained in Example 32 not only cutsultraviolet light but screens out near infrared light without reducingthe diffuse transmission in the visible region.

EXAMPLE 40

Fifteen parts by weight of the powder (P32) obtained in Example 32 and485 parts by weight of polycarbonate resin pellets were mixed andmelt-kneaded to obtain a molten composition having uniformly dispersedtherein 3 wt % of the fine particles. The composition was extruded intoa plate having a thickness of 1.5 mm. The resulting polycarbonate plate(A) was excellent in transparency, exhibited a UV screening effect and aheat ray screening effect, and presented an extremely attractiveappearance, assuming a pale pink or green color depending on the viewingangle or angle of light incidence.

COMPARATIVE EXAMPLE 13

A 1.5 mm thick polycarbonate plate (B) containing 3 wt % of fineparticles was prepared in the same manner as in Example 40, except forreplacing the powder (P32) with 15 parts by weight of zinc oxide fineparticles obtained by a French process (Aenka 1-Go, a product of SakaiChemical Industry Co., Ltd.). The resulting polycarbonate plate was awhite turbid plate with no characteristic in color.

EXAMPLE 41

Five parts by weight of the powder (P32) obtained in Example 32 and 95parts by weight of polyester resin pellets were mixed and melt-kneadedto obtain a polyester composition having uniformly dispersed therein 5wt % of the zinc oxide fine particles. The composition was extruded intoa sheet, and the extruded sheet was stretched to obtain a polyester filmhaving a thickness of 20 μm. The resulting film was a film havinguniformly and highly dispersed therein the fine particles. The film wastransparent, exhibited an excellent UV screening effect and a heat rayscreening effect, and presented an attractive appearance, assuming apale pink or green color depending on the viewing angle or angle oflight incidence.

COMPARATIVE EXAMPLE 14

A polyester film containing zinc oxide fine particles was obtained inthe same manner as in Example 41, except for replacing the powder (P32)obtained in Example 32 with zinc oxide fine particles obtained by aFrench process (Aenka 1-Go, a product of Sakai Chemical Industry Co.,Ltd.). The resulting film had a UV screening effect but was whiteturbid.

Observation of the surface of the films obtained in Example 41 andComparative Example 14 under a transmission electron microscope revealedthat the surface of the film obtained in Example 41 was covered withuniform and fine projections due to the fine particles, whereas thesurface of the film of Comparative Example 14 had a poor profile havingirregular projections containing coarse projections due to theagglomerated particles.

EXAMPLE 42

A polyester composition containing 5 wt % of fine particles was preparedin the same manner as in Example 41. The resulting polyester compositionwas melt-spun to obtain polyester fiber. The fiber had dispersed thereinthe fine particles uniformly and finely and had a heat ray screeningeffect as well as transparency and an excellent UV screening effect. Inaddition, the fiber had an excellent appearance similarly to the filmobtained in Example 41.

COMPARATIVE EXAMPLE 15

Polyester fiber containing zinc oxide fine particles was obtained in thesame manner as in Example 42, except for replacing the powder obtainedin Example 32 with zinc oxide fine particles obtained by a Frenchprocess (Aenka 1-Go, a product of Sakai Chemical Industry Co., Ltd.).The resulting fiber had a UV screening effect but was white turbid.

EXAMPLE 43

The dispersion (D32a) prepared in Example 32 was subjected tocentrifugation to remove the solvent. The resultant zinc oxide fineparticles containing a slight amount of the residual solvent componentwere dispersed in ion-exchanged water, followed by centrifugation again.The above operation was repeated several times, and the finally obtainedparticles were dispersed in ion-exchanged water to obtain 50 parts byweight of an aqueous dispersion containing 20 wt % of the fineparticles.

Fifty parts by weight of the aqueous dispersion were mixed with 20 partsby weight of an acrylic resin emulsion (Acryset® 285E, produced byNippon Shokubai Co., Ltd.; solids content: 50 wt %) as a binder toprepare a coating composition. Polyester fiber was soaked in the coatingcomposition and dried to obtain polyester fiber having the fineparticles at an add-on of 7.0 g/m². The resulting fiber not only cutultraviolet rays and heat rays effectively but presented an attractiveappearance similarly to the film obtained in Example 41.

COMPARATIVE EXAMPLE 16

Ten parts by weight of zinc oxide fine particles obtained by a Frenchprocess (Aenka 1-Go, a product of Sakai Chemical Industry Co., Ltd.)were mixed with 40 parts by weight of ion-exchanged water and dispersedby means of an ultrasonic homogenizer to give 50 parts by weight of anaqueous dispersion containing 20 wt % of the fine particles. Polyesterfiber having an add-on of 6.8 g/m² of the fine particles was obtained byusing the resulting aqueous dispersion in the same manner as in Example43. The resulting fiber exhibited a UV-screening effect but was whiteturbid.

EXAMPLE 44

A cosmetic (O/W type cream) containing the powder (P32) obtained inExample 32 was prepared according to the following formulation.

Formulation:

Aqueous Phase:

(a) Powder  6 parts by weight (b) Propylene glycol  5 parts by weight(c) Glycerin 10 parts by weight (d) Potassium hydroxide  0.2 part byweight (e) Ion-exchanged water 45 parts by weight

Oily Phase:

(f) Cetanol 5 parts by weight (g) Liquid paraffin 5 parts by weight (h)Stearic acid 3 parts by weight (i) Isostearyl myristate 2 parts byweight (j) Glycerol monostearate 2 parts by weight

The components (a) to (c) were mixed by stirring to prepare an aqueousphase, which was kept at 80° C. The components (f) to (j) were mixeduniformly to prepare an oily phase, which was kept at 80° C. The oilyphase was added to the aqueous phase, followed by stirring. The mixturewas emulsified by means of a homomixer, followed by cooling to roomtemperature to obtain cream. The resulting cream was clear and assumed apale pink color to produce an attractive appearance and also exhibitedan excellent UV screening effect and a heat ray screening effect.

COMPARATIVE EXAMPLE 17

Cream was prepared in the same manner as in Example 44, except forreplacing the powder obtained in Example 32 with zinc oxide fineparticles obtained by a French process (Aenka 1-Go, a product of SakaiChemical Industry Co., Ltd.).

The resulting cream had a UV screening effect but was opaque with a highdegree of whiteness.

COMPARATIVE EXAMPLE 18

Cream was prepared in the same manner as in Example 44, except forreplacing the powder obtained in Example 32 with thin plate like zincoxide fine particles having an average particle size of 0.8 μm and anaverage thickness of 0.1 μm.

The resulting cream was slightly transparent and had a UV screeningeffect but was white in tone and had no attractive appearance.

EXAMPLE 45

The powder (P32) obtained in Example 32 was mixed with ion-exchangedwater to prepare an aqueous dispersion containing 10 wt % of the fineparticles.

Separately, filter paper for quantitative determination (No. 5C, aproduct of Toyo Roshi K.K.) was beaten in a Niagara type beater to pulphaving a C.S. freeness of 400 cc. The above prepared aqueous dispersionwas added to the pulp to give a fine particle to pulp weight ratio of 1wt %. The resulting pulp slurry was diluted to a solids content of 0.1wt %, dehydrated in a TAPPI sheeting machine, and pressed to obtain aweb having a basis weight of 75 g/m², which was then dried in a rotarydrier at 100° C. to obtain paper containing 1 wt % of the fineparticles. The resulting paper presented an attractive appearance,assuming a pale pink or green color depending on the viewing angle orangle of light incidence, and also had a smooth surface.

COMPARATIVE EXAMPLE 19

Paper was prepared in the same manner as in Example 45, except forreplacing the powder obtained in Example 32 with zinc oxide particles inthe form of thin flat plate having an average particle size of 0.8 μmand an. average thickness of 0.1 μm. The resulting paper was white,presenting no beautiful appearance, and had a poor surface.

EXAMPLE I-1

In a 10 l glass-made reactor equipped with a stirrer, a droppingopening, a thermometer, and a reflux condenser, 0.3 kg of zinc oxidepowder and 36.3 g of indium acetate dihydrate were mixed with a mixedsolvent of 1.6 kg of acetic acid and 1.6 kg of ion-exchanged water. Themixture was heated up to 100° C. while stirring to prepare a uniformzinc-containing solution (AI-1).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 14 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 153° C. andmaintained at that temperature. To the heated alcohol was added dropwisethe whole amount of the zinc-containing solution (AI-1) kept at 100° C.over a 30-minute period by means of a constant delivery pump. Thetemperature of the alcohol-based system dropped from 153° C. to 131° C.After the dropwise addition, the inner temperature was increased. Whenthe temperature reached 168° C., 400 g of a 2-butoxyethanol solutioncontaining 36.9 g of lauric acid was added thereto over a period of 1minute, and the mixture was maintained at that temperature for 5 hoursto obtain 7.89 kg of a bluish gray dispersion (DI-1). The dispersion(DI-1) was a 3.5 wt % dispersion of thin and fine particles having anaverage particle size of 5 nm. The dispersed fine particles were X-raycrystallographically crystalline zinc oxide and had a metal oxidecontent of 94.5 wt % and contained indium at an atomic ratio of 3.0% tothe total number of metallic atoms.

The physical properties of the resulting dispersion and the fineparticles are shown in Table 10.

EXAMPLE I-2

A zinc-containing solution (AI-2) was prepared in the same manner as inExamine I-1, except for changing the kinds and amounts of the rawmaterials used in the zinc-containing solution (AI-1) of Example I-1 asshown in Table 8. Further, a dispersion (DI-2) was prepared in the samemanner as in Example I-1, except for changing the amount of2-butoxyethanol to 12 kg and using no lauric acid.

The physical properties of the resulting dispersion and the fineparticles are shown in Table 10.

To 227 parts by weight of the dispersion (DI-2) obtained above was added1 part by weight of octadecyltriethoxysilane, followed by stirring. Thesolvent was removed in an evaporator under reduced pressure at a bathtemperature of 130° C., and the residue was further dried in vacuo at100° C. to obtain 12 parts by weight of powder (PI-2-1).

EXAMPLE I-3

In the same 10 l glass-made reactor as used in Example I-1, equippedwith a stirrer, a dropping opening, a thermometer, and a refluxcondenser, 0.809 kg of zinc acetate dihydrate was mixed with a mixedsolvent of 2.2 kg of acetic acid and 2.2 kg of ion-exchanged water. Themixture was heated up to 100° C. while stirring to prepare a uniformzinc-containing solution (AI-3).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 8 kg of 2-butoxyethanoland 5 kg of ethylene glycol n-butyl ether acetate were charged, and theinner temperature was increased to 162° C. and maintained at thattemperature. To the heated alcohol solution was added dropwise the wholeamount of the zinc-containing solution (AI-3) kept at 100° C. over a30-minute period by means of a constant delivery pump. After thedropwise addition, the inner temperature was increased. When thetemperature reached 168° C., a uniform solution of 90.8 g of aluminumtris(sec-butoxide) in 400 g of 2-butoxyethanol was added thereto all atonce, and the mixture was maintained at 170° C. for 5 hours to obtain adispersion (DI-3).

The physical properties of the resulting dispersion and the fineparticles are shown in Table 10.

EXAMPLE I-4

A zinc-containing solution (AI-4) was prepared in the same manner as forthe zinc-containing solution (AI-1) of Examine I-1, except for changingthe kinds and amounts of the raw materials as shown in Table 8. Further,a dispersion (DI-4) was prepared in the same manner as in Example I-1,except for changing the amount of 2-butoxyethanol to 10.7 kg.

The physical properties of the resulting dispersion and the dispersedfine particles are shown in Table 10.

EXAMPLE I-5

In the same 10 l glass-made reactor as used in Example I-1, equippedwith a stirrer, a dropping opening, a thermometer, and a refluxcondenser, 0.30 kg of zinc oxide was mixed with a mixed solvent of 1.5kg of acetic acid and 1.5 kg of ion-exchanged water. The mixture washeated up to 80° C. while stirring to prepare a uniform zinc-containingsolution (AI-5).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 14 kg of 2-butoxyethanoland 60.6 g of ethylacetoacetatoaluminum diisopropylate were charged, andthe inner temperature was raised up to 150° C. and maintained at thattemperature. To the heated alcohol solution was added dropwise the wholeamount of the zinc-containing solution (AI-5) kept at 80° C. over a30-minute period by means of a constant delivery pump. After thedropwise addition, the inner temperature was increased to 170° C., atwhich the mixture was maintained for 5 hours to obtain a dispersion(DI-5).

The physical properties of the resulting dispersion and the fineparticles are shown in Table 10.

The fine particles contained in the dispersion (DI-5) were separatedfrom the dispersion medium by centrifugation, washed with methanol, anddried in vacuo (10 Torr) at 50° C. for 24 hours to obtain powder of thefine particles (PI-5).

The resulting powder (PI-5) had an average thickness of 0.025 μm, anaverage major axis of 0.08 μm, an L/B ratio of 2, a flatness of 3.2, ametal oxide content of 87.3 wt %, and an aluminum content of 5.5% interms of atomic ratio to the total number of metallic atoms. Theindividual fine particle of the powder consisted of a stack of 2 to 5thin plates (flakes) showing an X-ray diffraction pattern characteristicof crystalline zinc oxide.

COMPARATIVE EXAMPLE I-1

A dispersion of fine particles (DI-R1) was prepared in the same manneras in Example I-1, except that indium acetate was not used and theamount of 2-butoxyethanol was changed to 12.0 kg. The physicalproperties of the resulting dispersion and the fine particles are shownin Table 10.

EXAMPLE I-6

In a 10 l glass-made reactor equipped with a stirrer, a droppingopening, a thermometer, and a reflux condenser, 0.3 kg of zinc oxidepowder and 36.3 g of indium acetate dihydrate were mixed with a mixedsolvent of 1.6 kg of acetic acid and 1.6 kg of ion-exchanged water. Themixture was heated up to 100° C. while stirring to prepare a uniformzinc-containing solution (AI-6).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 158° C. andmaintained at that temperature. To the heated alcohol was added dropwisethe whole amount of the zinc-containing solution (AI-6) kept at 100° C.over a 60-minute period by means of a constant delivery pump. After thedropwise addition, the inner temperature was increased. When thetemperature reached 168° C., 500 g of a 2-butoxyethanol solutioncontaining 300.0 g of an acrylic polymer (methylmethacrylate-hydroxyethyl methacrylate-maleic acid copolymer=8/1/1 byweight; weight average molecular weight: 4,500) was added thereto over a1-minute period, and the mixture was maintained at 168° C. for 5 hoursto obtain 9.80 kg of a bluish gray dispersion (DI-6).

The dispersion (DI-6) was a 3.1 wt % dispersion of fine particles havingan average particle size of 20 nm. The dispersed fine particles wereX-ray crystallographically crystalline zinc oxide, having a metal oxidecontent of 55 wt % and containing indium at an atomic ratio of 3.0% tothe total number of metallic atoms. Observation under a transmissionelectron microscope provided confirmation that the individual fineparticles were metal oxide particles coated with the acrylic polymeradded.

The fine particles of the dispersion (DI-6) were separated from thedispersion medium by centrifugation, washed with isopropyl alcohol, anddried in vacuo (10 Torr) at 50° C. for 24 hours to obtain powder of thefine particles (PI-6).

It was confirmed that the fine particles of the powder (PI-6) weresubstantially equal to those in the dispersion.

The powder (PI-6) showed excellent dispersibility in organic solvents,such as alcohols (e.g., methanol, isopropyl alcohol, n-butanol, benzylalcohol, and 2-ethoxyethanol); ketones (e.g., methyl ethyl ketone,methyl isobutylketone, and cyclohexanone), esters (e.g., butyl acetateand ethyl acetate), and aromatic hydrocarbons (e.g., benzene andtoluene) and was easily re-dispersed in these solvents while retainingits single particle state.

EXAMPLE I-7

In a 10 l glass-made reactor equipped with a stirrer, a droppingopening, a thermometer, and a reflux condenser, 0.3 kg of zinc oxidepowder and 36.3 g of indium acetate dihydrate were mixed with a mixedsolvent of 1.6 kg of acetic acid and 1.6 kg of ion-exchanged water. Themixture was heated up to 100° C. while stirring to prepare a uniformzinc-containing solution (AI-7).

In a 20 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and an outlet for distillate gas andcould be heated by an external heating medium, 12 kg of 2-butoxyethanolwas charged, and the inner temperature was raised up to 158° C. andmaintained at that temperature. To the heated alcohol was added dropwisethe whole amount of the zinc-containing solution (AI-7) kept at 100° C.over a 30-minute period by means of a constant delivery pump. After thedropwise addition, the inner temperature was increased. When thetemperature reached 168° C., 400 g of a 2-butoxyethanol solutioncontaining 50.0 g of a methyl methacrylate-acrylic acid copolymer (9/1by weight; weight average molecular weight: 7,200) was added theretoover several seconds, and the mixture was further maintained at 168° C.for an additional 5 hour period to obtain 11.79 kg of a bluish graydispersion (DI-7). The dispersion (DI-7) was a 3.1 wt % dispersion ofspherical fine particles having a metal oxide content of 86.0 wt %, anaverage particle size of 0.5 μm, and a hollow structure in whichmicrocrystallites having a particle size of about 20 to 30 nm formed anouter shell of 0.2 μm in thickness.

The fine particles of the dispersion (DI-7) were separated from thedispersion medium by centrifugation, washed with isopropyl alcohol, anddried in vacuo (10 Torr) at 50° C. for 24 hours to obtain powder (PI-7)of the fine particles.

The resulting powder (PI-7) was spherical fine particles showing anX-ray diffraction pattern characteristic of crystalline zinc oxide,having an average particle size of 0.5 μm, and a metal oxide content of86.0 wt %, and an indium content at an atomic ratio of 3.0% to the totalnumber of metallic atoms. It was confirmed that the individual particleshad a hollow structure made by localization of metal oxide fineparticles having a diameter of about 25 nm and the methylmethacrylate-acrylic acid copolymer in the outer shell thereof. Thediameter of the hollow portion was 0.1 μm in average. Observation undera scanning electron microscope provided confirmation that the surface ofthe fine particles had fine unevenness.

The powder (PI-7) had excellent dispersibility in organic solvents, suchas alcohols (e.g., methanol, isopropyl alcohol, n-butanol, benzylalcohol, and 2-ethoxyethanol); ketones (e.g., methyl ethyl ketone,methyl isobutylketone, and cyclohexanone), esters (e.g., butyl acetateand ethyl acetate), and aromatic hydrocarbons (e.g., benzene andtoluene).

EXAMPLE I-8

Reaction was carried out in the same manner as in Example I-7, exceptfor using 72.5 g of indium acetate dihydrate in place of 36.3 g ofindium acetate dihydrate and using 800 g of a propylene glycol methylether acetate solution containing 30 g of polymethyl methacrylate (PMMA;weight average molecular weight: 60,000) in place of the 2-butoxyethanolsolution of the methyl methacrylate-acrylic acid copolymer, to obtain10.0 kg of a bluish gray dispersion (DI-8).

The fine particles of the dispersion (DI-8) were separated from thedispersion medium by centrifugation, washed with isopropyl alcohol, anddried in vacuo (10 Torr) at 50° C. for 24 hours to obtain powder (PI-8)of the fine particles.

The resulting powder (PI-8) was spherical fine particles showing anX-ray diffraction pattern characteristic of crystalline zinc oxide,having an average particle size of 3.0 μm, a metal oxide content of 90.1wt % and containing indium at an atomic ratio of 5.8% to the totalnumber of metallic atoms. It was confirmed that the individual particlescomprised PMMA having uniformly dispersed therein granular metal oxidefine particles having a particle size of about 20 nm.

EXAMPLE I-9

Reaction was carried out in the same manner as in Example I-7, exceptfor using 6.05 g of indium acetate dihydrate in place of 36.3 g ofindium acetate dihydrate and using 200 g of a 2-butoxyethanol solutioncontaining 7 g of lactic acid in place of the 2-butoxyethanol solutionof the methyl methacrylate-acrylic acid copolymer, to obtain a bluishgray dispersion (DI-9).

The fine particles of the dispersion (DI-9) were separated from thedispersion medium by centrifugation, washed with methanol, and dried invacuo (10 Torr) at 50° C. for 24 hours to obtain powder (I-9) of thefine particles.

The resulting powder (PI-9) was spherical fine particles showing anX-ray diffraction pattern characteristic of crystalline zinc oxide,having an average particle size of 1.2 μm, a metal oxide content of 96.0wt % and containing indium at an atomic ratio of 0.5% to the totalnumber of metallic atoms. The individual particles had a hollowstructure in which the diameter of the hollow portion was 0.6 μm, andthe outer shell consisted of densely stacked thin plates of metal oxidefine particles having a major axis of 0.3 μm and a flatness of 18.

Further, the powder (PI-9) had excellent dispersibility in polarsolvents, such as water, alcohols (e.g., methanol, isopropyl alcohol,n-butanol, benzyl alcohol, and 2-ethoxyethanol); ketones (e.g., methylethyl ketone, methyl isobutylketone, and cyclohexanone), and esters(e.g., butyl acetate and ethyl acetate).

EXAMPLE I-10

A zinc-containing solution (AI-10) was prepared in the same manner as inExample I-1, except for changing the kinds and amounts of the rawmaterials used in the zinc-containing solution (AI-1) of Example I-1 asshown in Table 9. A dispersion (DI-10) was prepared from thezinc-containing solution (AI-10) in the same manner as in Example I-1,except for changing the amount of the 2-butoxyethanol to 12 kg andreplacing lauric acid with 30.0 g of monoethanolamine.

The physical properties of the resulting dispersion and the fineparticles of the dispersion are shown in Table 10.

TABLE 8 Zinc-Containing Solution Alcohol Solution Additive SolutionMonocar- Metal Metal Metal Zinc boxylic (M) (M) (M) Source Acid OthersCompound Alcohol Compound Compound Others Example [Amount] [Amount][Amount] [Amount] [Amount] [Amount] [Amount] [Amount] No. (kg) (kg) (kg)(g) (kg) (g) (g) (g) I-1 zinc oxide acetic water indium 2-butoxy- — —lauric [0.30] acid [1.60] acetate ethanol acid [1.60] dihydrate [14.0][36.9] [36.3] I-2 zinc oxide acetic water indium 2-butoxy- — — — [0.285]acid [2.20] hydroxide ethanol basic [2.20] (In₂O₃.5H₂O) [12.0] zinc[20.33] carbonate* [0.0203] I-3 zinc acetate acetic water — 2-butoxy —aluminum — dihydrate acid [2.20] ethanol tris(sec- [0.809] [2.20] [8.0]butyrate) ethylene [90.8] glycol n-butyl ether acetate [5.0] I-4 zincoxide acetic water indium 2-butoxy- — — lauric [0.30] acid [1.60]hydroxide ethanol acid [2.20] (In₂O₃.5H₂O) [10.7] [36.9] [13.55] I-5zinc oxide acetic water — 2-butoxy- ethyl- — — [0.30] acid [1.500]ethanol acetoacetato- [1.50] [14.0] aluminum diisopropylate [60.6] Note:*ZnO content: 74.0 wt %

TABLE 9 Zinc-Containing Solution Alcohol Solution Additive SolutionMonocar- Metal Metal Metal Zinc boxylic (M) (M) (M) Source Acid OthersCompound Alcohol Compound Compound Others Example [Amount] [Amount][Amount] [Amount] [Amount] [Amount] [Amount] [Amount] No. (kg) (kg) (kg)(g) (kg) (g) (g) (g) Compa- zinc oxide acetic water — 2-butoxy- — —lauric rative [0.30] acid [1.60] ethanol acid Example [1.60] [12.0][36.9] I-1 I-6 zinc oxide acetic water indium 2-butoxy- — — methyl[0.30] acid [1.60] acetate ethanol methacrylate- [1.60] dihydrate [12.0]hydroxyethyl [36.3] methacrylate- maleic acid copolymer [300.0] I-7 zincoxide acetic water indium 2-butoxy- — — methyl [0.30] acid [1.60]acetate ethanol methacrylate- [1.60] dihydrate [12.0] acrylic acid[36.3] copolymer [50.0] I-8 zinc oxide acetic water indium 2-butoxy — —polymethyl [0.30] [1.60] [1.60] acetate ethanol methacrylate dihydrate[12.0] [30.0] [72.5] I-9 zinc oxide acetic water indium 2-butoxy- — —lactic acid [0.30] acid [1.60] acetate ethanol [7] [1.60] dihydrate[12.0] [6.05]  I-10 zinc oxide acetic water indium 2-butoxy- — —monoethanol- [0.30] acid [2.20] hydroxide ethanol amine [2.20](In₂O₃.5H₂O) [12.0] [30.0] [5.42]

TABLE 10 Visible Concn. of Metal Light Particles Metal (M)/ AverageX-ray Heat Electric Trans- Ex- Dis- in Dis- Oxide Total Parti- ParticleDiff- UV Ray con- mission ample persion persion Content Metal cle Sizefraction Cutting Cutting duc- (Trans- No. No. (wt %*) (wt %) (atom %)Shape (μm) Pattern Power Power tivity parency) I-1 Di-1 3.5 94.5 3.0thin 0.005 ZnO A +++ +++ +++ plate crystal I-2 Di-2 4.4 95.8 2.9granular 0.01 ZnO A +++ +++ +++ crystal I-3 Di-3 5.5 92.0 9.2 granular0.21 ZnO B ++ ++ ++ crystal I-4 Di-4 5.0 95.0 2.0 granular 0.01 ZnO A+++ ++ +++ crystal I-5 Di-5 3.6 87.3 5.5 thin 0.08(1) ZnO A ++ + ++plate 0.025(t) crystal I-6 Di-6 3.1 55.0 3.0 granular 0.02 ZnO A +++ +++++ crystal Compa- Di-RI 3.7 94.8 0 granule 0.02 ZnO A + − +++ rativecrystal I-1 I-7 Di-7 3.1 86.0 3..0 granular 0.50 ZnO B +++ ++ + crystalI-8 Di-8 3.3 90.1 5.8 granular 3.0 ZnO B +++ ++ + crystal I-9 Di-9 5.896.0 0.5 granular 1.2 ZnO B ++ ++ + crystal  I-10  Di-10 3.2 87.0 0.8granular 0.003 ZnO A ++ +++ ++ crystal Note: *Concentration as convertedto metal oxides

The dispersions (DI-1) and (DI-R1) obtained in Example I-1 andComparative Example I-1 were each concentrated in an evaporator underreduced pressure at a bath temperature of 130° C. to have a particleconcentration of 10 wt % to prepare a concentrated dispersion (DI-1C)and (DI-RC), respectively. To 100 parts by weight of the concentrateddispersion was added 1.11 part by weight of an acrylic resin solution(Alloset 5210 produced by Nippon Shokubai Co., Ltd.; solids content: 45wt %), followed by stirring for 2 hours to prepare a coatingcomposition.

Each coating composition was applied by spin coating to a Pyrex glassplate having thereon a comb type electrode made of gold by vacuumevaporation, dried at room temperature, and heated at 50° C. to providea dry film (DI-1M) or (DI-RM). Each coating film was a homogeneous filmhaving a thickness of 1.0 μm.

After the dried film was allowed to stand at 20° C. and 60% RH for 1hour with light shielded, the surface resistivity of the film wasmeasured under the above environmental conditions with Electrometer 617(produced by Kesley Corp.). The results were as follows.

DI-1M 2.7 × 10¹¹ Ω per square DI-RM 3.9 × 10¹⁴ Ω per square

The surface resistivity of the film Di-1M was also measured after it wasallowed to stand at 20° C. and at the relative humidity shown below for1 hour with light shielded. The results were as follows.

Surface Resistivity Relative Humidity (Ω per square) 20% 1.9 × 10¹¹ 60%2.7 × 10¹¹ 85% 2.8 × 10¹¹

Coating compositions were prepared using the dispersions (DI-2) to(DI-5) obtained in Examples I-2 to I-5 and applied to a glass plate toform a coating film having a thickness of 1 μm in the same manner asdescribed above. The surface resistivity of the resulting film wasmeasured at 20° C. and 60% RH. As a result, the surface resistivity(unit: Ω per square) of every coating film was on the order of 10¹¹ or10¹². It was also confirmed that the surface resistivity was constantirrespective of humidity similarly to the case of Example I-1.

These results provide confirmation that the fine particles of thedispersions obtained in Examples I-1 to I-5 were more conductive thanconventional zinc oxide particles. It was also confirmed that theconductivity of these particles was independent on humidity. Therefore,the fine particles (or dispersions) obtained by the invention aresuitable materials of an antistatic film.

Powder samples were obtained from the dispersions (DI-2) and (DI-R1)obtained in Example I-2 and Comparative Example I-1 in the same manneras described above. The results of powder X-ray diffractometry on theresulting powder samples are shown in FIG. 10, in which the abscissaindicates a diffraction angle (2θ; °), and the ordinate the intensity(cps). As is shown in FIG. 10, it can be seen that both Di-2 and Di-R1show sharp peaks assigned to ZnO.

COMPARATIVE EXAMPLE I-2

In 500 g of ion-exchanged water was dissolved 35.0 g of ammoniumbicarbonate to prepare a solution A.

In ion-exchanged water was dissolved 6.1778 g of aluminum sulfatehydrate (Al₂(SO₄)₃.nH₂O: n=14 to 18) to prepare a solution B.

A hundred grams of zinc oxide prepared by a French process (Aenka 1-Go,a product of Sakai Chemical Industry Co., Ltd.) were added to 180 g ofion-exchanged water to obtain a slurry C.

Further, 1.00 g of silica fine powder (Aerosil 200, produced by NipponAerosil K.K.) was added to 50 g of ion-exchanged water, followed bystirring to prepare a dispersion D.

The solution B was added to the solution A while stirring at roomtemperature, whereupon the mixture became an emulsion. The stirring ofthe emulsion was continued for 10 minutes.

In a 1 l glass-made reactor which was equipped with a stirrer, adropping opening, a thermometer, and a reflux condenser and could beheated by an external heating medium, the slurry C was charged, and theabove-prepared emulsion was added thereto through the dropping openingwhile stirring at room temperature. The heating medium temperature wasset at 80° C., and heating was started. About 30 minutes later when theinner temperature reached 61° C., the dispersion D was added, followedby stirring for 1 hour under heating. One hour later, when the innertemperature reached 76.6° C., heating was stopped, and the system wasallowed to cool while continuing stirring. When the inner temperaturedropped to room temperature, the whole amount of the slurry wassubjected to vacuum filtration. The thus separated fine particles werethoroughly washed with ion-exchanged water, dried in vacuo at 50° C. for12 hours and then dried in vacuo at 100° C. for 4 hours to give whitepowder.

The X-ray diffraction pattern of the resulting white powder showed notonly the diffraction peaks assigned to ZnO but also peaks assigned toimpurity, which was ascribable to basic zinc carbonate Zn₄CO₃(OH)₆.H₂O.It was thus confirmed that ZnO had low crystalline properties. The X-raydiffraction pattern of the powder is shown in FIG. 11.

COMPARATIVE EXAMPLE I-3

In 50 g of ion-exchanged water were dissolved 8.3753 g of zinc chloride(ZnCl₂) and 0.3167 g of aluminum chloride (AlCl₃.6H₂O) to obtain auniform solution. A 14 wt % ammonia aqueous solution was added dropwiseto the solution while stirring at room temperature. The dropwiseaddition was stopped when the pH of the system reached 8.21. The amountof the 14 wt % aqueous ammonia added was 20.0 g.

After the dropwise addition, the mixture was stirred for 10 minutes,followed by filtration. The filter cake was thoroughly washed withwater, followed by centrifugation to recover the fine particles. Theparticles were vacuum dried at 50° C. for 12 hours and then dried invacuo at 100° C. for 4 hours to furnish white powder.

The X-ray diffraction pattern of the resulting white powder showed nopeak assigned to ZnO. The X-ray diffraction pattern of the powder isshown in FIG. 11.

COMPARATIVE EXAMPLE I-4

White powder was prepared in the same manner as in Comparative ExampleI-2. The resulting white powder was put in a calcining furnace andheated from room temperature to 640° C., kept at this temperature for 1hour in a nitrogen atmosphere, and cooled to room temperature to givegrayish white powder.

It was confirmed by X-ray diffractometry that the resulting powder wasZnO crystals. The X-ray diffraction pattern of the powder is shown inFIG. 11.

The powder was formulated into a coating composition of the followingcomposition, and the coating composition was applied to a glass platesubstrate to obtain a coated article (II-R4C) having a 3.1 μm thickcoating film. The resulting coated article (II-R4C) was white turbid andhad low transparency to visible light, having a haze as high as 78%. Itexhibited UV screening properties but no heat ray screening properties.The spectral transmission curve of the coated article (II-R4C) is shownin FIG. 12.

Formulation of Coating Composition:

Powder 10 parts by weight 2-Butoxyethanol 90 parts by weight Acrylicresin solution* 50 parts by weight *Alloset 5247 (produced by NipponShokubai Co., Ltd.; solid content: 45 wt %) was diluted with toluene toa solids content of 20 wt %.

Preparation of Coating Composition:

The powder was added to 2-butoxyethanol and dispersed in an ultrasonichomogenizer for 20 minutes. The acrylic resin solution was addedthereto, followed by stirring for 2 hours. The mixture was furtherdispersed in an ultrasonic homogenizer for 20 minutes to obtain acoating composition.

COMPARATIVE EXAMPLE I-5

White powder was obtained in the same manner as in Comparative ExampleI-3. The powder was heated from room temperature to 640° C. in anitrogen atmosphere in a calcining furnace, maintained at 640° C. for 1hour, and cooled to room temperature to obtain slightly greenishgray-tinted powder.

As a result of X-ray diffractometry, it was confirmed that the resultingpowder was ZnO crystals. The X-ray diffraction pattern of the powder isshown in FIG. 11, in which the abscissa indicates a diffraction angle(2θ; °), and the ordinate the intensity (cps).

The powder was formulated into a coating composition in the same manneras in Comparative Example I-4, and the coating composition was appliedto a glass plate to obtain a coated article (II-R5C) having a 3.2 μmthick film. The coated article (II-R5C) was white turbid and had lowtransparency to visible light, having a haze as high as 83%. Itexhibited UV screening properties but no heat ray screening properties.The spectral transmission curve of the coated article (II-R5C) is shownin FIG. 12.

EXAMPLE II-1

The dispersion (DI-1) obtained in Example I-1 was concentrated in anevaporator under reduced pressure at a bath temperature of 130° C. tohave a particle concentration of 10 wt % to prepare a concentrateddispersion (DI-1C).

An acrylic resin solution (Alloset 5210 produced by Nippon Shokubai Co.,Ltd.; solids content: 45 wt %) was diluted with toluene to a resinconcentration of 20 wt %. To 50 parts by weight of the diluted resinsolution was added 100 parts by weight of the concentrated dispersion(DI-1C), followed by stirring to prepare 150 parts by weight of acoating composition (II-1).

EXAMPLE II-2

The dispersion (DI-2) obtained in Example I-2 was concentrated in anevaporator under reduced pressure at a bath temperature of 130° C. tohave a particle concentration of 10 wt % to prepare a concentrateddispersion (DI-2C).

The concentrated dispersion (DI-2C) was separated by centrifugation intoa precipitate of the fine particles and the solvent (supernatantliquid). The precipitate was added to ion-exchanged water and dispersedin a sand mill to obtain an aqueous dispersion (DI-2W) having finelydispersed therein 10 wt % of the fine particles.

To 100 parts by weight of an aqueous solution containing 10 wt % of avinyl resin (Poval R2105, produced by Kuraray Co., Ltd.) was added 100parts by weight of the aqueous dispersion (DI-2W), followed by stirringto obtain a coating composition (II-2) containing 5 wt % of the fineparticles and 5 wt % of the binder.

EXAMPLE II-3

The dispersion (DI-1) obtained in Example I-1 was concentrated in anevaporator under reduced pressure at a bath temperature of 130° C. tohave a particle concentration of 10 wt % to prepare a concentrateddispersion (DI-1C).

In a 4-necked flask equipped with a reflux condenser, a stirrer, and athermometer were charged successively 24 parts by weight of isopropylalcohol, 16 parts by weight of water, and 0.005 part by weight of 35%hydrochloric acid. To the mixture were further added 10 parts by weightof methyltrimethoxysilane and 30 parts by weight of tetraethoxysilanewhile stirring, and the mixture was heated at 80° C. for 2 hours,followed by cooling. The resulting mixture (x) was a uniform solutionhaving a non-volatile content of 17.0 wt %.

Twelve parts by weight of the mixture (x) were added to 80 parts byweight of the concentrated dispersion (DI-1C) while stirring to preparea coating composition (II-3).

EXAMPLE II-4

In the same manner as in Example II-2, an aqueous dispersion (DI-2W)having finely dispersed therein 10 wt % of fine particles was preparedfrom the dispersion (DI-2) obtained in Example I-2.

To 20 parts by weight of an aqueous solution containing 10 wt % of avinyl resin (Poval 205, produced by Kuraray Co., Ltd.) was added 100parts by weight of the aqueous dispersion (DI-2W), and 20 parts byweight of an aqueous solution containing 1.23 part by weight of copperacetate monohydrate was further added thereto, followed by stirring.Ultrasonication of the mixture gave a coating composition (II-4).

The coating compositions (II-1) to (II-4) obtained in Examples II-1 toII-4 were applied to various substrates with a bar coater and dried toobtain coated articles (II-1C1), (II-1C2), (II-2C), (II-3C), and(II-4C), respectively.

The film formation conditions, the thickness of the coating film, andthe optical characteristics of the coated articles are shown in Table 11below.

TABLE 11 Physical and Optical Properties of Coated Article UV FilmForming Conditions Film Heat Cutting Trans- Total Coat- Drying Thick-Ray Cut Power mission Trans- Coated ing Com- Coating Con- ness (2 μm)(Trans- (600 nm) mission Haze Article position Substrate Method ditions(μm) (%) mission) (%) (%) (%) II-1C1 II-1 glass bar  80° C., 1.2 17 B(6%) 85 87 20 coater 30 min II-1C2 II-1 glass bar  80° C., 5.5 54 A (0%)73 76 35 coater 30 min II-2C II-2 acrylic bar 100° C., 3.7 55 A (0%) 8384  9 resin coater 30 min plate II-3C II-3 PC bar 200° C., 0.8 42 B (2%)78 80 29 plate coater 30 min II-4C II-4 PET bar 110° C., 1.2 30 A (1%)84 85 13 film coater  5 min

The coating film of every coated article was homogeneous and screenedout ultraviolet rays and heat rays while having excellent transparencyto visible light.

The sunlight transmission and visible light transmission of the coatedarticles (II-1C1) and (II-1C2) were measured to give the followingresults. The results provide confirmation that the coating film wastransparent and yet exhibited heat insulating properties.

Sunlight Visible Light Trans- Trans- mission (a) mission (b) (a) − (b)(%) (%) (%) II-1C1 70.22 71.00 +0.78 II-1C2 82.99 84.84 +1.85 glassplate 89.82 91.52 −1.70 (substrate)

The coated article (II-3C) was hard, having a surface hardness of 6(pencil hardness), and had a surface resistivity of 1×10⁹ Ω per square,which indicates antistatic properties.

COMPARATIVE EXAMPLE II-1

A coating composition (II-R1) was prepared in the same manner as inExample II-1, except for replacing the dispersion (DI-1) as used inExample II-1 with the dispersion (DI-R1) obtained in Comparative ExampleI-1. The coating composition (II-R1) was applied and dried on the sameglass substrate as used in the coating articles II-1 and II-2 in thesame manner as for the coating articles II-1 and II-2 to obtain a coatedarticle (II-R1C) having a 6.3 μm thick film containing ZnO fineparticles. The resulting coated article (II-R1C) was effective inscreening ultraviolet rays but exhibited no heat ray screening effect.

The spectral transmission curves of the coated articles (II-1C1) and(II-1C2) obtained in Examples and the coated article (II-R1C) obtainedin Comparative Example (II-1) are shown in FIG. 9, in which the abscissaindicates the wavelength of incident light (nm), and the ordinate thetransmission (%). The spectral transmission curve of the glass substrateis also shown in FIG. 9.

EXAMPLE II-5

In the same manner as in Example II-2, an aqueous dispersion (DI-2W)having finely dispersed therein 10 wt % of fine particles was preparedfrom the dispersion (DI-2) obtained in Example I-2.

A hundred parts by weight of the aqueous dispersion were mixed with 20parts by weight of an acrylic resin emulsion (Acryset® ES-285E, producedby Nippon Shokubai Co., Ltd.; solids content: 50 wt %) as a binder toprepare a coating composition (II-5). Polyester fiber was soaked in thecoating composition and dried to obtain polyester fiber having the fineparticles at an add-on of 4.0 g/m². The resulting fiber was excellent intransparency while cutting ultraviolet rays and heat rays.

COMPARATIVE EXAMPLE II-5

In the same manner as in Example II-2, an aqueous dispersion havingfinely dispersed therein 10 wt % of fine particles was prepared from thedispersion (DI-R1) obtained in Comparative Example I-1.

A hundred parts by weight of the aqueous dispersion were mixed with 20parts by weight of an acrylic resin emulsion (Acryset® ES-285E, producedby Nippon Shokubai Co., Ltd.; solids content: 50 wt %) as a binder resinto prepare a coating composition (II-R5). Polyester fiber was soaked inthe coating composition and dried to obtain polyester fiber having thefine particles at an add-on of 4.2 g/m². The resulting fiber wasexcellent in transparency and cut ultraviolet rays but had no heat rayscreening effect.

EXAMPLE II-6

In the same manner as in Example II-2, an aqueous dispersion (DI-2W)having finely dispersed therein 10 wt % of fine particles was preparedfrom the dispersion (DI-2) obtained in Example I-2.

A hundred parts by weight of the aqueous dispersion were mixed with 30parts by weight of an acrylic resin emulsion (Acryset® ES-285E, producedby Nippon Shokubai Co., Ltd.; solids content: 50 wt %) as a binder resinto prepare a coating composition (II-5). Polyster fiber was soaked inthe coating composition and dried to obtain polyester fiber having thefine particles at an add-on of 3.0 g/m². The resulting fiber wasexcellent in transparency while cutting ultraviolet rays and heat rays.

EXAMPLE II-7

Ten parts by weight of the powder (PI-2-1) obtained in Example 1-2 and90 parts by weight of polypropylene (PP) pellets were melt-kneaded toobtain PP pellets (A) containing 10 wt % of the powder (PI-2-1).

A double-layered PP film was prepared using an extruder equipped with afeed block die for multilayer extrusion as follows. PP pellets (B)containing no fine particles were fed to the main extruder and melted at220° C., while the PP pellets (A) were fed to the secondary extruder andmelted at 180° C. Both resins were extruded while adjusting theextrusion rate of each extruder to obtain a laminate sheet composed of aPP (A) layer (powder-containing layer) and a PP (B) layer. The extrudedlaminate sheet was stretched to obtain an OPP film (biaxially stretchedpolypropylene film) composed of a 8 μm thick PP (A) layer and a 20 μmthick PP (B) layer.

The resulting film was a multilayer film having a thin layer (A) inwhich the fine particles were uniformly and highly dispersed, which wasexcellent in visible light transmitting properties while exhibitingexcellent UV screening and heat ray screening properties.

EXAMPLE II-8

Fifty parts by weight of the powder (PI-6) obtained in Example I-6 and50 parts by weight of polyethylene terephthalate (PTE) pellets weremelt-kneaded to prepare PET pellets (A) containing 50 wt % of the powder(PI-6).

A double-layered PET film was prepared using the same extruders andstretching machine as used in Example II-7 as follows. PET pellets (B)containing no fine particles were fed to the main extruder and melted at310° C., while the PET pellets (A) were fed to the secondary extruderand melted at 280° C. Both resins were extruded while adjusting theextrusion rate of each extruder to obtain a laminate sheet composed of aPET (A) layer (powder-containing layer) and a PET (B) layer. Theextruded laminate sheet was stretched to obtain a PET film composed of a2 μm thick PET (A) layer and a 20 μm thick PET (B) layer.

The resulting film was a multilayer film having a thin layer (A) inwhich the fine particles were uniformly and highly dispersed, which wasexcellent in visible light transmitting properties while exhibitingexcellent UV screening and heat ray screening properties.

EXAMPLE II-9

The dispersion (DI-4) obtained in Example I-4 was concentrated in anevaporator under reduced pressure at a bath temperature of 130° C. toprepare a concentrated dispersion (DI-4C) having a particleconcentration of 25 wt %.

A coating composition was prepared using an acrylic resin solution(Alloset 5858, produced by Nippon Shokubai Co., Ltd.; solid content: 60wt %) as a binder component as follows.

Seventeen parts by weight of the acrylic resin solution, 40 parts byweight of the concentrated dispersion (DI-4C), and 23 parts by weight ofn-butanol were mixed by stirring and dispersed in an ultrasonichomogenizer to prepare 80 parts by weight of a coating composition(II-9).

EXAMPLE II-10

In the same manner as in Example II-2, an aqueous dispersion (DI-4W)having finely dispersed therein 10 wt % of fine particles was preparedfrom the dispersion (DI-4) obtained in Example I-4.

To 100 parts by weight of an aqueous solution containing 10 wt % of avinyl resin (Poval 205, produced by Kuraray Co., Ltd.) was added 100parts by weight of the aqueous dispersion (DI-4W), followed by stirring.The mixture was dispersed in an ultrasonic homogenizer to obtain acoating composition (II-10).

EXAMPLE II-11

To 80 parts by weight of the concentrated dispersion (DI-4C) was added150 parts by weight of the mixture (x) while stirring, followed bystirring. The mixture was dispersed in an ultrasonic homogenizer toobtain a coating composition (II-11).

The resulting coating compositions (II-9) to (II-11) were applied tovarious substrates with a bar coater and dried to obtain coated articles(II-9C1), (II-9C2), (II-9C3), (II-9C4), and (II-4C), respectively.

The total transmission and haze of the substrates used are shown below.

Total Transmission Haze Substrate (%) (%) glass 92 <0.1 PET 89 2.0 OPP88 3.2 PC 84 3.0

The film formation conditions, the thickness of the coating film, andthe optical characteristics of the coated articles are shown in Table 12below.

TABLE 12 Film Heat Total Coating Thick- Ray Cut UV Cutting Trans- CoatedCompo- Drying ness (2 μm) Power (Trans- mission Haze Article sitionSubstrate Conditions (μm) (%) mission) (%) (%) 9C1 II-9 glass 80° C., 30sec 3.2 50 A (0%) 90 0.4 9C2 II-9 PET ″ 3.1 47 A (1%) 88 2.2 9C3 II-9OPP ″ 3.3 52 B (2%) 84 4.0 9C4  II-10 PC 120° C., 10 min 2.5 40 B (2%)82 3.5 4C  II-11 PC 200° C., 10 min 4.0 55 A (0%) 90 0.4

EXAMPLE III-1

Five parts by weight of the powder (PI-6) obtained in Example I-6 and995 parts by weight of polycarbonate resin pellets were mixed andmelt-kneaded to obtain a molten mixture having uniformly dispersedtherein 0.5 wt % of the fine particles. The composition was extruded toobtain a polycarbonate plate having a thickness of 2.0 mm. The resultingpolycarbonate plate had highly dispersed therein the fine particles andexhibited excellent visible light transmitting properties, having atotal transmission of 85% or higher, UV screening properties, and heatray screening properties.

EXAMPLE III-2

Twenty-five parts by weight of the powder (PI-7) obtained in Example I-7and 475 parts by weight of methacrylic resin pellets were mixed andmelt-kneaded to obtain a molten composition having uniformly dispersedtherein 5 wt % of the fine particles. The composition was extruded toobtain a methacrylic resin sheet having a thickness of 2 mm. Theresulting sheet had highly dispersed therein the fine particles and hada total transmission of 83% and a haze of 86%, exhibiting high visiblelight transmitting properties and excellent diffuse transmittingproperties, and also had excellent UV and heat ray screening effects.

COMPARATIVE EXAMPLE III-1

A 2 mm thick polycarbonate plate containing 0.5 wt % of fine particleswas obtained in the same manner as in Example III-1, except forreplacing the powder (PI-6) as used in Example III-1 with zinc oxidefine particles prepared by a French process (Aenka 1-Go, a product ofSakai Chemical Industry Co., Ltd.). The resulting polycarbonate platewas found to contain the fine particles non-uniformly in a secondarilyagglomerated state. As compared with the one obtained in Example 111-1,the polycarbonate plate was white turbid, lacking transparency, and hada low UV screening effect. A heat ray screening effect was not observed.

EXAMPLE III-3

Two parts by weight of the powder (PI-6) obtained in Example I-6 and 98parts by weight of polyester resin pellets were mixed and melt-kneadedto obtain a polyester composition having uniformly dispersed therein 2wt % of the zinc oxide fine particles. The composition was extruded intoa sheet, and the extruded sheet was stretched to obtain a polyester filmhaving a thickness of 40 μm. The resulting film was a film having thefine particles uniformly and highly dispersed therein which wasexcellent in visible light transmitting properties, UV screeningproperties, and heat ray screening properties.

COMPARATIVE EXAMPLE III-2

A 40 μm thick polyester film containing 2 wt % of fine particles wasobtained in the same manner as in Example III-3, except for replacingthe powder (PI-6) as used in Example III-3 with zinc oxide fineparticles prepared by a French process (Aenka 1-Go, a product of SakaiChemical Industry Co., Ltd.). The resulting film was found to containthe fine particles in a secondarily agglomerated state and therefore hada low UV screening effect and was white turbid, lacking transparency. Noheat ray screening effect was observed.

The section of the films obtained in Example III-3 and ComparativeExample III-2 was observed through a transmission electron microscope.As a result, the film obtained in Example III-3 was a practicallyhomogeneous film in which the fine particles were highly dispersed,whereas the film obtained in Comparative Example III-2 had a poorsurface profile with coarse projections due to agglomeration of the fineparticles. Besides, the film had insufficient abrasion resistance andscratch resistance on account of gaps between the fine particles and thePET matrix.

EXAMPLE III-4

A polyester composition containing 2 wt % of the powder (PI-6) wasprepared in the same manner as in Example III-3. The resulting polyestercomposition was melt-spun to obtain polyester fiber. The fiber haduniformly and highly dispersed therein the fine particles and exhibitedtransparency and excellent UV and heat ray screening properties.

COMPARATIVE EXAMPLE III-3

Polyester fiber containing zinc oxide fine particles was obtained in thesame manner as in Example III-4, except for replacing the powder (PI-6)as used in Example III-4 with zinc oxide fine particles prepared by aFrench process (Aenka 1-Go, a product of Sakai Chemical Industry Co.,Ltd.). The resulting fiber was found to contain the fine particles in asecondarily agglomerated state and therefore had a low UV screeningeffect and was white turbid, lacking transparency. No heat ray screeningeffect was observed.

EXAMPLE IV-1

In the same manner as in Example II-2, an aqueous dispersion (DI-1W)having finely dispersed therein 10 wt % of fine particles was preparedfrom the dispersion (DI-1) obtained in Example I-1. A cosmetic (O/W typecream) containing the aqueous dispersion was prepared according to thefollowing formulation.

Formulation:

Aqueous Phase:

(a) Aqueous dispersion 50 parts by weight (b) Propylene glycol  5 partsby weight (c) Glycerin 10 parts by weight (d) Potassium hydroxide  0.2part by weight

Oily Phase:

(e) Cetanol 5 parts by weight (f) Liquid paraffin 5 parts by weight (g)Stearic acid 3 parts by weight (h) Isostearyl myristate 2 parts byweight (i) Glycerol monostearate 2 parts by weight

The components (a) to (d) were mixed by stirring to prepare an aqueousphase, which was kept at 80° C. The components (e) to (i) were mixeduniformly to prepare an oily phase, which was kept at 80° C. The oilyphase was added to the aqueous phase, followed by stirring. The mixturewas emulsified by means of a homomixer, followed by cooling to roomtemperature to obtain cream. The resulting cream was clear and yetexcellent in UV screening effect and heat ray screening effect.

COMPARATIVE EXAMPLE IV-1

Cream was prepared in the same manner as in Example IV-1, except forreplacing the aqueous dispersion (DI-1W) as used in Example IV-1 with 50parts by weight of an aqueous dispersion containing 5 parts by weight ofzinc oxide fine particles obtained by a French process (Aenka 1-Go, aproduct of Sakai Chemical Industry Co., Ltd.) in a concentration of 10wt %.

The resulting cream had an insufficient UV screening effect on accountof poor dispersion of the fine particles and was opaque with a highdegree of whiteness. No heat ray screening properties was observed.

[Example of Paper Making]

EXAMPLE V-1

In the same manner as in Example II-2, an aqueous dispersion (DI-2W)having finely dispersed therein 10 wt % of fine particles was preparedfrom the dispersion (DI-2) obtained in Example I-2.

Separately, filter paper for quantitative determination (No. 5C, aproduct of Toyo Roshi K.K.) was beaten in a Niagara type beater to pulphaving a C.S. freeness of 400 cc. The above prepared aqueous dispersionwas added to the pulp to give a fine particle to pulp weight ratio of 1wt %. The resulting pulp slurry was diluted to a solids content of 0.1wt %, dehydrated in a TAPPI sheeting machine, and pressed to obtain aweb having a basis weight of 75 g/m², which was then dried in a rotarydrier at 100° C. to obtain paper containing 1 wt % of the fineparticles. The fine particles being dispersed satisfactorily, theresulting paper had excellent UV screening properties, a heat rayscreening effect, and excellent surface smoothness. Further, the paperhardly attracted dirt, etc.

COMPARATIVE EXAMPLE V-1

Paper was prepared in the same manner as in Example V-1, except forreplacing the aqueous dispersion (DI-2W) as used in Example V-1 with anaqueous dispersion containing 10 wt % of zinc oxide fine particlesobtained by a French process (Aenka 1-Go, a product of Sakai ChemicalIndustry Co., Ltd.). The resulting paper had a low UV screening effectdue to secondary agglomeration of the fine particles. The surfaceconditions were poor with coarse projections due to the agglomeratedparticles. The paper had no heat ray screening properties and easilyattracted dirt, etc.

Industrial Utility

The process for producing zinc oxide fine particles according to thepresent invention is a highly productive process, in which zinc oxidefine particles are obtained with controlled particle size, controlledparticle shape, controlled surface conditions, and a controlled state ofdispersion or agglomeration. The zinc oxide fine particles obtained bythe process exhibit excellent functions and characteristics as fineparticles, such as UV screening properties and transparency, and aretherefore useful in coating compositions, coated articles, resincompositions, resin molded articles, paper, cosmetics, and the like.

The zinc oxide-polymer composite particles according to the presentinvention have UV screening power, controlled visible light transmittingproperties and controlled light diffusing properties, and excellentdispersibility. They are useful in coating compositions, coatedarticles, resin compositions, resin molded articles, paper, cosmetics,diffusers for-back-lighting liquid crystal displays, and the like.

The inorganic compound particles according to the present invention haveon the surface a cluster of thin plate like zinc oxide crystals whosetips project outward. Based on such unique geometrical characteristicsnot heretofore achieved, the particles exhibit abnormal lighttransmitting properties and can be used in coating compositions, coatedarticles, resin compositions, resin molded articles, paper, cosmetics,and the like to provide products having near infrared ray screeningproperties without impairing attractiveness and transparency of theproducts.

The zinc oxide-based particles according to the present invention mainlycomprise zinc oxide endowed with heat ray screening properties andelectrical conductivity in addition to excellent UV screeningproperties. Therefore, they can be used in coating compositions, coatedarticles, resin compositions, resin molded articles, paper, cosmetics,and the like to furnish products which exhibit excellent transparency,screen out ultraviolet rays and infrared rays, such as heat rays, andhave controlled conductivity, such as antistatic properties.

What is claimed is:
 1. Zinc oxide-based particles comprising a metaloxide co-precipitate containing, as a metallic component, at least oneelement additive selected from the group consisting of the group IIIBmetal elements and the group IVB metal elements and zinc, having a zinccontent of 80 to 99.9% in terms of the ratio of the number of zinc atomsto the total number of the atoms of said metallic components, and havingX-ray crystallographically exhibiting zinc oxide crystalline properties.2. Zinc oxide-based particles according to claim 1, wherein said elementadditive is indium and/or aluminum.
 3. A cosmetic containing 0.1% byweight or more of the zinc oxide-based particles described in claim 1.4. Zinc oxide-polymer composite particles which comprise zinc oxide fineparticles and a polymer, the proportion of said zinc oxide fineparticles being 50 to 99% by weight based on the total weight of saidzinc oxide fine particles and said polymer, and the composite particleshaving an outer shell composed of a mixture and/or a composite of saidzinc oxide fine particles and said polymer with the inside of said outershell being hollow.
 5. Composite particles comprising: (i) zincoxide-based particles comprising a metal oxide co-precipitatecontaining, as a metallic component, (a) at least one element additiveselected from the group consisting of metals of Group IIIB and metals ofGroup IVB, and (b) zinc, and having a zinc content of 80 to 99.9% interms of the ratio of the number of zinc atoms to the total number ofthe atoms of said metallic components, and having X-raycrystallographically exhibiting zinc oxide crystalline properties, and(ii) a polymer.
 6. Inorganic compound particles containing 60 to 100% byweight of zinc oxide and having on their surface a cluster of thin platezinc oxide crystals with their tips projecting outward.
 7. Inorganiccompound particles according to claim 6, wherein said particles arehollow.
 8. Inorganic compound particles according to claim 6, whereinsaid particles are porous.
 9. Inorganic compound particles according toclaim 6, wherein said zinc oxide crystals are thin plates having aflatness of 2 to
 200. 10. Inorganic compound particles according toclaim 9, wherein said thin plates have a major axis of 5 to 1,000 nm.11. A cosmetic containing 0.1% by weight or more of the inorganiccompound particles described in claim
 6. 12. An antimicrobial agentcomprising the inorganic compound particles described in claim
 6. 13. Anadsorbent comprising the inorganic compound particles described in claim6.
 14. A process for producing zinc oxide fine particles comprising:forming a mixture comprising a zinc source, a carboxyl-containingcompound, and an alcohol, and heating said mixture to form saidparticles.
 15. A process for producing zinc oxide fine particlesaccording to claim 14, wherein said heating step is carried out in thepresence of a compound additive containing one or more than one atomicgroup of at least one kind selected from the group consisting of acarboxyl group, an amino group, a quaternary ammonio group, an amidogroup, an imido bond, a hydroxyl group, a carboxylic acid ester bond, aurethane group, a urethane bond, a ureido group, a ureylene bond, anisocyanate group, an epoxy group, a phosphoric acid group, a metallichydroxyl group, a metallic alkoxy group, and a sulfonic acid group inthe molecule thereof and having a molecular weight of less than 1,000.16. A process for producing zinc oxide fine particles according to claim14, wherein said heating step is carried out in the presence of carbondioxide and/or a carbonic acid source.
 17. Zinc oxide fine particlesproduced by a process described in claim
 14. 18. A process for producingzinc oxide-based particles comprising: forming a mixture comprising azinc source, a carboxyl-containing compound, at least one elementadditive selected from the group consisting of the group IIIB metalelements and the group IVB metal elements, and an alcohol, and heatingsaid mixture at a temperature of 100° C. or above to form saidparticles.
 19. A process for producing zinc oxide-based particlesaccording to claim 18, wherein said group IIIB metal element is indiumand/or aluminum.
 20. A process for producing inorganic compoundparticles having on their surface a cluster of zinc oxide crystals withtheir tip projecting outward, which comprises: forming a mixturecomprising a zinc source, a carboxyl-containing compound, lactic acid ora compound thereof, and an alcohol, and heating said mixture at atemperature of 100° C. or above to form said particles.
 21. A processfor producing zinc oxide-polymer composite particles, which comprises:forming a mixture comprising a zinc source, a carboxyl-containingcompound, a polymer, and an alcohol at a temperature of 1000 or above;and heating said mixture to form said particles.